The best I've been able to do with standard tools is some crude outlines in Powerpoint. Helps me with the color selection and some of the details, but not if you are trying to complement any unique shapes/outlines that you didn't/can't generate in PP. It can be a struggle to get the color shade correct when you are trying to work with the basic pallet. On this example, I used Klasskote orange on the fuse which was brighter and redder than the PP choice. On the positive side, with a couple of keystrokes, you can make copy after copy and just edit the colors until you see what you like using side by side comparisons. After a couple of different planes, you sort of have a "kit" of numbers, stripes, checks, etc.
On this particular "Trash Can Cardinal" I was happy with it except that I chose a SIG lightweight iron-on which had poor adhesion, even to itself. And, it didn't hold up well. So now I need to recover it if it is to fly again. Since I rebuild the plane out of several club members donations to the trash can, I'm not real enthused about more repairs....