explain what the colors mean

[lmj0011]

I agree it's obvious what the green and red colors mean, but the yellow may be questionable to some.
Doesn't seem like it would hurt to place a legend, explaining the colors suppose to mean, at the bottom of the diagram.

[fippo]

there is no hard definition. Nothing of this is backed by any tests.

[thislooksfun]

@fippo that in itself is a good thing to add to the page.