Once you do color space correct color mixing you realize that people actually expect the wrong result, i.e. the result you get from mixing in sRGB and then you have to make the rendering output visually more "correct" by making it incorrect. One of the cases where the correct computation is the wrong answer.

Heck, that's what people expect with CSS for example.

My reference renderer has been Core Graphics. If it looks like CG I assume it's OK - and if it's not OK I'm in good company ;-)

You can switch between CG and Rasterizer in the demo app using the 0 key to see the difference for yourself.