Here's a great source of color markings and insignia for hundreds of aircraft, all eras. http://wp.scn.ru/en/markings
The categories are WWI, Between Wars, WWII, Cold War, Modern.
Once you select an era it gets pretty specific, Attack, Fighter, Bomber, Recon, Transport
etc. Then model, variant, country used by (captured aircraft used by another country are shown), front or theater of operation. Takes quite a few clicks to get to the thumbnails but it's worth it!
The color reproductions are sharp, most have only the profile but some are 2-view. Lots of odd and obscure aircraft.
Check it out!