What on earth does red+yellow mean? "It's about to be green"?

This is why modern green lights have a blueish tint to them. At least here in the US, older green lights were more of a pure green, and that meant for red-green colorblind people it was much harder to differentiate between red lights and green lights. But in this image you can see that the slight blue tint makes them pretty different.

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I found it like this elsewhere, alright? If you or anyone else has a higher quality version, please feel free to share it and I'll replace the OP with it.