What's the evidence that the colors were added later?

[Rafal]

I find it hard to imagine that certain illustrations should have looked like this:

This looks unfinished.

And again don't know if it was discussed but here and for example You are not allowed to view links. Register or Login to view. there are some parallel "stripes"



They are only partly coloured and look like unfinished rainbows to me:


I am not sure if the artist:
- didn't know it is a rainbow
- didn't care to colour it properly
- lacked paint or time
- other

But what did seems consistent for me with other referrences