Red on Green is Readable

Red on green is readable, including by people with red-green blindness, it just depends on the shade of red or green (This is #DC0000 on #82FEA9).
And we can predict it will be readable because the brightness difference, which on the above example is 159 STW* brightness difference and 141 YIQ brightness difference (see Readable Text in Colour), and this is above the breakpoint for brightness difference, irrespective of hue, so even if you have red-green blindness it will be readable. (Try it on the colour blindness tester:
We could convert the same brightness levels to monochrome using the reliable STW* formula, so as to simulate how someone with no colour perception at all would see it. This is #707070 on #E5E5E5, which also has a brightness difference of 159. (It has a W3C guideline colour difference of 351, so should be out of readability range according to the W3C guidelines. But as I say so often on these pages, the W3C guidelines are easily discredited with even the cursoriest of researches.)
Brightness difference is the key to readability, and it is so significant, that you can ignore the issue of designing for people with colourblindness. If the brightness level difference indicates that the text will be readable, it will be readable by people with colour recognition deficiencies, because there’s adequate difference in brightness, irrespective of the hue.
Where there is inadequate difference in brightness for the text to be considered readable, that doesn’t mean that the text is unreadable, but it may be to varying levels hard to read. There’s more on this on my Close Colour Readability page.


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