Well, I think this thing came out looking pretty much the way I wanted it to look - alien but not garish. I considered making the colours a lot darker/grungier, but this pretty much is how HPL described the Yithians, for once something that wasn't shadowy and ichorous.
In response to javi's comment: the grey parts are just grey, except where they blend into coloured areas. As for the base, I didn't even really want to have one - it's a free-standing creature - but I think it worked out all right, and it'll save me from a bunch of CoolMiniOrNot comments saying "if this had a base I'd like it better" so I made it out of card stock and foamcore. The plain octagonal floor slabs are as described in the original text.