I’m building a lot of planes lately from foam. To dress it up and give it some colours I like to use packing tape. It’s basically the same stuff you use to tape up boxes. I use the clear stuff to add a protective layer for the foam and then I use coloured tape to decorate it. I wasn’t able to find any locally. Mind you there is coloured duct tape but that stuff is too heavy for light foam planes.
The come in lots of colours so you can add racing stripes to that F-117 or F-22 jet.
I found a web site that sells them very cheap. I got 6 rolls for under $10. Also shipping to Canada wasn’t too bad either, around $10.
Check out fastpack.net.