diff --git a/documentation/dsl.md b/documentation/dsl.md
index e317757f..8bc0d57a 100644
--- a/documentation/dsl.md
+++ b/documentation/dsl.md
@@ -207,10 +207,8 @@ Colors may be specified using
 - [Keywords](https://www.w3.org/wiki/CSS/Properties/color/keywords) like `red`, `white` or `black`
 - Short hexadecimal colors like `#d13` for crimson red
 - Long hexadecimal colors like `#e6e6fa` for lavender
-- RGB values like `rgb(160, 82, 45)` for sienna brown
-- HSL values like `hsl(120, 60, 70)` for pastel green
-
-SonicWeave doesn't have percentages so the CSS color `hsl(120, 60%, 70%)` is spelled without the percent signs.
+- RGB values like `rgb(160 82 45)` for sienna brown
+- HSL values like `hsl(120deg 60% 70%)` for pastel green
 
 ## Code comments
 
diff --git a/src/grammars/base.pegjs b/src/grammars/base.pegjs
index 11c42dd5..57ab9cca 100644
--- a/src/grammars/base.pegjs
+++ b/src/grammars/base.pegjs
@@ -57,6 +57,10 @@ RGB4
 RGB8
   = $('#' HexDigit|6|)
 
+CSSNumber
+  = [+-]? ('0' / ([1-9] DecimalDigit*)) ('.' DecimalDigit*)?
+  / [+-]? '.' DecimalDigit+
+
 IdentifierName
   = $(IdentifierStart IdentifierPart*)
 
diff --git a/src/grammars/sonic-weave.pegjs b/src/grammars/sonic-weave.pegjs
index 7381bc55..1678c6be 100644
--- a/src/grammars/sonic-weave.pegjs
+++ b/src/grammars/sonic-weave.pegjs
@@ -1266,6 +1266,7 @@ NotANumberLiteral
 InfinityLiteral
   = InfinityToken { return { type: 'InfinityLiteral' }; }
 
+// RGB and HSL use modern CSS syntax, no legacy support
 ColorLiteral
   = value: (@RGB8 / @RGB4) {
     return {
@@ -1273,6 +1274,18 @@ ColorLiteral
       value,
     };
   }
+  / 'rgb' 'a'? '(' __ CSSNumber '%'? __ CSSNumber '%'? __ CSSNumber '%'? (__ '/' __ __ CSSNumber '%'?)? __ ')' {
+    return {
+      type: 'ColorLiteral',
+      value: text(),
+    };
+  }
+  / 'hsl' 'a'? '(' __ CSSNumber 'deg'? __ CSSNumber '%'? __ CSSNumber '%'? (__ '/' __ CSSNumber '%'?)? __ ')' {
+    return {
+      type: 'ColorLiteral',
+      value: text(),
+    };
+  }
 
 VulgarFraction 'vulgar fraction'
   = '¼' / 'q' / '½' / 's' / '¾' / 'Q' / [⅐-⅞] / ''
diff --git a/src/interval.ts b/src/interval.ts
index 5736bf28..6e96aecb 100644
--- a/src/interval.ts
+++ b/src/interval.ts
@@ -57,10 +57,10 @@ export class Color {
 
   /**
    * SonicWeave representation of the CSS color.
-   * @returns A string without percentage signs.
+   * @returns The color value as a string.
    */
   toString() {
-    return this.value.replace(/%/g, '');
+    return this.value;
   }
 }
 
diff --git a/src/parser/__tests__/expression.spec.ts b/src/parser/__tests__/expression.spec.ts
index 11d21237..9ccc65b5 100644
--- a/src/parser/__tests__/expression.spec.ts
+++ b/src/parser/__tests__/expression.spec.ts
@@ -604,16 +604,16 @@ describe('SonicWeave expression evaluator', () => {
   });
 
   it('supports hsl colors', () => {
-    const greenish = evaluate('hsl(123, 45, 67)') as Color;
-    expect(greenish.value).toBe('hsl(123.000, 45.000%, 67.000%)');
-    expect(greenish.toString()).toBe('hsl(123.000, 45.000, 67.000)');
+    const greenish = evaluate('hsl(123deg 45% 67%)') as Color;
+    expect(greenish.value).toBe('hsl(123deg 45% 67%)');
+    expect(greenish.toString()).toBe('hsl(123deg 45% 67%)');
     const retry = evaluate(greenish.toString()) as Color;
     expect(retry.value).toBe(greenish.value);
   });
 
   it('supports rgb color labels and reprs', () => {
     const lightFifth = evaluate('repr(3/2 rgb(200, 222, 256))');
-    expect(lightFifth).toBe('(3/2 rgb(200.000, 222.000, 256.000))');
+    expect(lightFifth).toBe('(3/2 rgb(200.000 222.000 256.000))');
   });
 
   it('can concatenate strings', () => {
@@ -642,9 +642,9 @@ describe('SonicWeave expression evaluator', () => {
     expect(nothing).toHaveLength(0);
   });
 
-  it('interpretes cents as linear decimals in rgba', () => {
-    const faded = evaluate('rgba(255, 255, 255, 0.5)') as Color;
-    expect(faded.value).toBe('rgba(255.000, 255.000, 255.000, 0.50000)');
+  it('has rgba syntax', () => {
+    const faded = evaluate('rgba(255 255 255 / 0.5)') as Color;
+    expect(faded.value).toBe('rgba(255 255 255 / 0.5)');
   });
 
   it('preserves labels based on preference (left)', () => {
diff --git a/src/parser/__tests__/sonic-weave-ast.spec.ts b/src/parser/__tests__/sonic-weave-ast.spec.ts
index 9bf8da4c..1da07e09 100644
--- a/src/parser/__tests__/sonic-weave-ast.spec.ts
+++ b/src/parser/__tests__/sonic-weave-ast.spec.ts
@@ -1186,6 +1186,25 @@ describe('SonicWeave Abstract Syntax Tree parser', () => {
       ],
     });
   });
+
+  it('parses CSS hsl literals', () => {
+    const ast = parseSingle('hsl( -.5deg -50%  10 / 40%  )');
+    expect(ast).toEqual({
+      type: 'ExpressionStatement',
+      expression: {
+        type: 'ColorLiteral',
+        value: 'hsl( -.5deg -50%  10 / 40%  )',
+      },
+    });
+  });
+
+  it('parses CSS rgb literals', () => {
+    const ast = parseSingle('rgba(255 50% 5 / .5)');
+    expect(ast).toEqual({
+      type: 'ExpressionStatement',
+      expression: {type: 'ColorLiteral', value: 'rgba(255 50% 5 / .5)'},
+    });
+  });
 });
 
 describe('Automatic semicolon insertion', () => {
diff --git a/src/parser/__tests__/stdlib.spec.ts b/src/parser/__tests__/stdlib.spec.ts
index 7467d55a..f85e9595 100644
--- a/src/parser/__tests__/stdlib.spec.ts
+++ b/src/parser/__tests__/stdlib.spec.ts
@@ -710,7 +710,7 @@ describe('SonicWeave standard library', () => {
 
   it('preserves labels when rotating', () => {
     const scale = parseSource(
-      '5/4 yellow "third";3/2 white "fifth";2/1 rgba(255, 255, 255, 0.5) "octave";rotate()'
+      '5/4 yellow "third";3/2 white "fifth";2/1 rgba(255, 255, 255, 0.5e) "octave";rotate()'
     );
     expect(scale).toHaveLength(3);
     expect(scale[0].valueOf()).toBeCloseTo(6 / 5);
@@ -718,7 +718,7 @@ describe('SonicWeave standard library', () => {
     expect(scale[0].label).toBe('fifth');
     expect(scale[1].valueOf()).toBeCloseTo(8 / 5);
     expect(scale[1].color?.value).toBe(
-      'rgba(255.000, 255.000, 255.000, 0.50000)'
+      'rgba(255.000 255.000 255.000 / 0.50000)'
     );
     expect(scale[1].label).toBe('octave');
     expect(scale[2].valueOf()).toBeCloseTo(2);
@@ -1101,10 +1101,10 @@ describe('SonicWeave standard library', () => {
   it('colors intervals based on deviation from 12ed2', () => {
     const scale = expand('5/4;3/2;7/4;2;edColors()');
     expect(scale).toEqual([
-      '5/4 hsl(310.729, 100.000, 50.000)',
-      '3/2 hsl(7.038, 100.000, 50.000)',
-      '7/4 hsl(247.773, 100.000, 50.000)',
-      '2 hsl(0.000, 100.000, 50.000)',
+      '5/4 hsl(310.729deg 100.000% 50.000%)',
+      '3/2 hsl(7.038deg 100.000% 50.000%)',
+      '7/4 hsl(247.773deg 100.000% 50.000%)',
+      '2 hsl(0.000deg 100.000% 50.000%)',
     ]);
   });
 
diff --git a/src/stdlib/builtin.ts b/src/stdlib/builtin.ts
index 7480d9d8..51ad1098 100644
--- a/src/stdlib/builtin.ts
+++ b/src/stdlib/builtin.ts
@@ -2394,15 +2394,12 @@ help.__node__ = builtinNode(help);
 
 // CSS color generation
 function cc(x: Interval, fractionDigits = 3) {
-  if (x?.node?.type === 'CentsLiteral') {
-    return x.totalCents().toFixed(fractionDigits);
-  }
   return x.value.valueOf().toFixed(fractionDigits);
 }
 
 function rgb(red: Interval, green: Interval, blue: Interval) {
   requireParameters({red, green, blue});
-  return new Color(`rgb(${cc(red)}, ${cc(green)}, ${cc(blue)})`);
+  return new Color(`rgb(${cc(red)} ${cc(green)} ${cc(blue)})`);
 }
 rgb.__doc__ =
   'RGB color (Red range 0-255, Green range 0-255, Blue range 0-255).';
@@ -2411,7 +2408,7 @@ rgb.__node__ = builtinNode(rgb);
 function rgba(red: Interval, green: Interval, blue: Interval, alpha: Interval) {
   requireParameters({red, green, blue, alpha});
   return new Color(
-    `rgba(${cc(red)}, ${cc(green)}, ${cc(blue)}, ${cc(alpha, 5)})`
+    `rgba(${cc(red)} ${cc(green)} ${cc(blue)} / ${cc(alpha, 5)})`
   );
 }
 rgba.__doc__ =
@@ -2420,7 +2417,7 @@ rgba.__node__ = builtinNode(rgba);
 
 function hsl(hue: Interval, saturation: Interval, lightness: Interval) {
   requireParameters({hue, saturation, lightness});
-  return new Color(`hsl(${cc(hue)}, ${cc(saturation)}%, ${cc(lightness)}%)`);
+  return new Color(`hsl(${cc(hue)}deg ${cc(saturation)}% ${cc(lightness)}%)`);
 }
 hsl.__doc__ =
   'HSL color (Hue range 0-360, Saturation range 0-100, Lightness range 0-100).';
@@ -2434,7 +2431,7 @@ function hsla(
 ) {
   requireParameters({hue, saturation, lightness, alpha});
   return new Color(
-    `hsla(${cc(hue)}, ${cc(saturation)}%, ${cc(lightness)}%, ${cc(alpha, 5)})`
+    `hsla(${cc(hue)}deg ${cc(saturation)}% ${cc(lightness)}% / ${cc(alpha, 5)})`
   );
 }
 hsla.__doc__ =
diff --git a/src/stdlib/public.ts b/src/stdlib/public.ts
index 7002f3e8..a4134a9d 100644
--- a/src/stdlib/public.ts
+++ b/src/stdlib/public.ts
@@ -365,7 +365,7 @@ export function centsColor(this: ExpressionVisitor, interval: Interval) {
   const h = octaves * 360;
   const s = Math.tanh(1 - octaves * 0.5) * 50 + 50;
   const l = Math.tanh(octaves * 0.2) * 50 + 50;
-  return new Color(`hsl(${h.toFixed(3)}, ${s.toFixed(3)}%, ${l.toFixed(3)}%)`);
+  return new Color(`hsl(${h.toFixed(3)}deg ${s.toFixed(3)}% ${l.toFixed(3)}%)`);
 }
 
 // Prime colors for over/under.
@@ -426,7 +426,7 @@ export function factorColor(this: ExpressionVisitor, interval: Interval) {
       b += prgb[2] * m;
     }
   }
-  return new Color(`rgb(${tanh255(r)}, ${tanh255(g)}, ${tanh255(b)})`);
+  return new Color(`rgb(${tanh255(r)} ${tanh255(g)} ${tanh255(b)})`);
 }
 
 /**