Hello Philp,
If you look on the General Modelling Discussion section of this forum, you'll find a post entitled 'Free Online Image Gallery' , thread posted by Ron USMC.
Follow the link in his post, as I've just uploaded a picture I took of Chinook ZA707 (EV) at RAF Mildenhall in 91.
A really good reference (if you can get hold of a copy in the USA) is a UK magazine 'Model Aircraft Monthly' Volume 2, Issue 2 (February 2003) which has a 7 page photo feature on RAF Chinook colours, with about 12 shots of Desert Storm machines, in 3 or 4 different schemes. It's a back issue, but you should be able to get hold of a copy at www.sampublications.com.
Hope this is of use, but I don't envy you hand painting that colour scheme!
Cheers,
Rob Monfea.