Pictures,and colored penciles
I have an RV-4 that I built, and had several different paint "ideas", and about the time I was ready to commit, I came across 4 gallons of pure white PPG Desothane being "discarded" from my day job...so ,since I was doing the paint myself,"free" was a beautiful start. After my all white RV-4 was flying, I grabbed some 1/8" green masking tape, and layed out several different paint schemes , took pictures from different angles,and printed full sheet copies..then grabbed colored pencils and colorized my black and white copies. This gave a very real and accurate idea of what things would look exactly like. That was 5 years ago, and I stuck with all white and named my plane "Casper". But I still have those, maybe someday, schemes if I ever want to try them. The -4 has unique lines, that can really look good with the cowl cheeks when designed correctly.