For those of you still looking for perceptually uniform colour maps, including rainbows, check out the work of Peter Kovesi [1].
Personally, I'm still on the lookout for the 'perfect' colourmap that allows me to plot line graphs with a moderate number of curves (up to, say, nine) such that they are all distinct (i.e., nicely 'spaced' in colour) but have identical lightness -- which I'm assuming is the same thing as greyscale equivalent -- so as not to emphasize any one curve over another. Of course, the curves would then be indistinguishable when printed out in greyscale, but that's not important to me.
A colleague of mine directed me to the work of Maureen Stone [2], but I get the feeling that those colours are not perceptually identical (not that I've checked...).
[1] https://peterkovesi.com/projects/colourmaps/ [2] http://ksrowell.com/blog-visualizing-data/2012/02/02/optimal...