Here's what has been working for me using only 2 MS programs.. MS Works Word Processor (used to print decal sheets) and MS Paint (design, color, and size the decal)....you don't necessarily need a White bodied car.
Some of these I ripped from the net...the smaller contingency decals....the others I designed, colored and sized using MS Paint...the 7's , the 427 C.I's, Omers, Henry's, Hayes House of H.P...the 427's and Omers are in a Red block that I trimmed down before applying.... Using MS Paint I was able to match the color hue (Red) that is the body color. Printed on White decal paper.
Here is what Omers looks like after I trimmed the excess Red part of the decal...the 427's on the hood have the same appearance...same as with the Topeka, Kansas that's under Hayes House of H.P