Horamakhet, I've just discovered that a KGV 1d red was indeed printed on pink paper!
This item is described thus:
Description: PERFORATED 'OS': 1d carmine perforated plate proof on gummed watermarked pink paper BW70PP(5)
I found the stamp listed at this location:
http://allisastamps.koolhost.com/kgv1dredpage2.htmSo far, this webpage is the only reference to such an issue I've come across. The pink paper is also mentioned in the certificate of authenticity that goes with the stamp.
Apparently, it's a very rare proof (just 4 examples known).
I'll update this thread if I find out anything more.