Personally I prefer substances to be what you might call 'natural' colours of really old fashioned wam - the colours you typically find in desserts - white, yellow, brown, pink etc - not such a big fan of the 'artificials' - blues, purples and greens, which seem to be in vogue these days (although I know there's a long history of loving the green slime).

Good topic. I voted artificial simply because I prefer stark contrasts but, overall, I would say I don't really have a preference as long as it works. I'm not hung up on the 'green' slime thing at all but I'm very aware that this is probably the most divisive preference for some in terms of shade and texture.