That’s one of those envisioning things at play. Most people can’t detect slight variations in color even when they can see them, so while you do indeed see a gradient your memory tends to trim it down to less variance. It’s estimated that we can discern around a million distinct colors, but remembering that is difficult for all but a very small number of people. Most of just remember the idea of a rainbow and then reconstruct the imagery later.
MjHomeschool t1_iuhah3z wrote
Reply to comment by imgroxx in ELI5: Why are the colours in rainbows in separate lines? by Oheligud
That’s one of those envisioning things at play. Most people can’t detect slight variations in color even when they can see them, so while you do indeed see a gradient your memory tends to trim it down to less variance. It’s estimated that we can discern around a million distinct colors, but remembering that is difficult for all but a very small number of people. Most of just remember the idea of a rainbow and then reconstruct the imagery later.