Hi Andrew! Colour really only has meaning to us within the visible spectrum, outside that it's really just wavelength even though we invent descriptions like ultraviolet and infrared. So I don't think we can have any idea of the "true" colour of Uranus unless we have visual sensitivity to the whole range of the electromagnetic spectrum.
I had a bit of a play-around with the optical (visual) spectrum of Uranus once, obtained with a DSLR and an SA100 grating. I suspect that what I did was self-fulfilling in that the DSLR sensor 'assigns' a colour to Uranus, I then split that colour with a grating, and then put that back together to give a colour for Uranus!
Anyway, it was a bit of fun!
Cheers -