I'm not sure, but I noticed it when I was there, the three Huss ride's near Colossos (I think they've been relocated from elstwhere in the park) are all plain white and green - it is'nt an "offensive" scheme, but it does get a bit boring, especially when their SLC and Corkscrew have white track too. ( Long story short: not sure)
I suppose if they painted them though, they'd look out of place with everything else, the corkscrew's neutrel scheme complement's it's magnificent lake side setting well IMO, so that would certainly be a shame for me! http://www.rcdb.com/ig986.htm?picture=1
^ That look's fantastic IMO, not so much themeing, but such a great setting and the neat garden's complement it well!
Limit look's crap!