Hi Burt:
I did find a few more things since I wrote that last post... Monogram aviation has a few copies of their color chip charts left. These are the same color chip pages that they use in their books. The only shortcoming is that this covers US aircraft only. I bought one from their website... I think it was $38. Pricey, but high quality. If you can't afford their books, this is the next best thing.
I bought three really neat out-of-print books that include color info. One is the IPMS color cross-reference guide by David Klauss. I picked this up on bookfinder.com for about $15, but I had to get it from overseas. The only bad thing about this book is that it has no color samples itself, but relies on the US color spec. It's not much help without it. When it was printed, the FS 595a US govt color spec was current, nowadays they use the 595B (I understand that the difference is a few new colors and numbers... the old numbers and colors are supposed to be identical between 595a and 595b, but don't quote me on that).
The Federal color spec used to be a piece of cake to get... in 1991 it cost a whopping $5.50. Now the FS595b spec costs something like $90... I should've invested in chip-chart futures. I bought a 595a from an ebay seller in Canada, but it's been a month now, and still no color spec. If you do buy the cross reference, realize that if it comes combined with the Federal color spec, it's worth A LOT more, 'cause it's a PITA to buy them separately.
Another ebay score was Markings and Camouflage Systems of Luftwaffe Aircraft in WW2, by Karl Reiss Jr. I somehow managed to get this for $19.50, and some sellers have this same book listed with Bookfinder for $64, so I definately got lucky here. (but if you look around, other sellers have this at $20) It's a very good, though slim book, in English, 110 pages, and (of particular importance to me) includes a single page of color standards from November 1941. This is lithographed (actual paint samples would be better) but it gives me an actual look at 04 gelb yellow or 66 schwarzgrau black-grey, for example. It's one of a three-volume set.
My third ebay score was Aircraft Camouflage and Markings 1907-1954 Written and Compiled by Bruce Robertson, printed in 1959. This one I got for $4.99, with shipping it was nine bucks. Average price for this one is around $25. It's a pretty good book... lots of detail, though I suspect there might be some errors here and there. Some of these subjects have been extensively researched since this book came out. It's heavy on the Great Britain side, and a little slim on the other powers, and doesn't contain information about color shades.
There's lots of info out there if you look for it. The good thing is that most of this stuff holds its value pretty well, so you can always sell back if something doesn't meet your needs.
Hope this helps, good luck with your search, and let me know if you find anything else out about colors!
Best
BG