Oh. It’s that time of year already. Time to hate on the rainbow color scale, which is still prevalent but equally less useful than alternatives. Matt Hall provides (scientific!) reasons for looking to scales that don’t include the full spectrum and some solutions.
We know what kind of colourmaps are good for interpretation: those that increase linearly and monotonically in brightness, with no jumps or stripes of luminance. I’ve linked to lots of places where you can read about these — see the end of the post. You already know one perceptual colourmap: the humble Greyscale. But there are lots of others, so let’s start with one of them.