[firmgently]

It's complementary, which is a different word and has a very specific meaning when it comes to colour theory (a colour's complement is the colour directly opposite it on a colour wheel) https://en.wikipedia.org/wiki/Complementary_colors

[rhgg]

They don't appear to be complementary either. The complement to #ee4035 is in the cyan range (~5cf7fa). You can get this by hand.

Convert #ee4035 to rgb(234, 64, 53). Subtract those values from max RGB domain (255) and take square root of difference of squares. i.e sqrt(255^2 - 238^2) etc.

You end up with rgb(92, 247, 250), or the cyan color mentioned above. You can also check this in several other complementary calculators.

I could be missing something.

[wdutch]

that's the rgb compliment[1], this app uses the traditional colour wheel[2]

1: https://en.wikipedia.org/wiki/Complementary_colors#Colors_pr... 2: https://en.wikipedia.org/wiki/Color_wheel

[rhgg]

TIL. I shouldn't have skipped art class. Thanks for the sources.

[pushpop]

Ahhh I see. Thank you for the correction.