Raventutor:
You seem to primarily build Commonwealth kits by the questions in your previous posts. So to answer your question partly. Paint of all colours as required for military uses was of priority issue. However a review of many photos of vehicles and armour most "Nicknames" appear to be in white or light gray. As I previously mentioned paint was not hard to get at first for military uses, however once the Liberation of the Continent began paint could and would have been subject to two factors supply and demand. So some paint could have been scavenged from the local area. A reference for you to consider at the end of the war a Regiment of Sherman M4A4's and Firefly's were repainted with captured surplus Kriegsmarine Grey paint.
As far as Pin-Ups and Caricatures being painted on armour, so far I can not find any supporting references of such items. This seems to be an Air Force style of painting. That's not to say it never happened, however you'd need to find reference to portray a specific vehicle.
Of course it is your kit to build and paint as you want. A popular cartoonist/comic strip writer for the Canadian overseas newspaper was a fellow named Bing. He created the character Herbie and there are a couple books that show all of his cartoons from the Italian campaign and the European Theatre that may give you some ideas for a "Canadianized" cartoon for the side of your armour. Or it may inspire a diorama.
If you are intent on using some of the Disney or Warner Bros. cartoons you can find references to which characters were around by either a visit to the video store or a search of the internet for the 1940's era of cartoon characters. There were tons of them.
You will probably come across "Kilroy was here" as a popular theme during your search. This was a common graffiti across the theatres of Italy and Europe. The real Kilroy was an inspector in the dockyards that built the Liberty ships and other transport vessels. Mr. Kilroy would check the work of dockyard workers and would "sign" Kilroy was here as proof of his checks throughout the construction of the ship. So many soldiers, sailors and airmen on the ships over to the war saw this slogan throughout the ships that eventually they ended up scrolling it on everything and anything.
Just a bit of useless/useful trivia for you.
Hope this helps with the build.
Cheers;
Gregory