Early one, I put some dabs of color on a few sticks. Used some exterior trim enamel. Rustoleum oil based. Wouldn't recommend it. To heavy for detail, colors really garish, at least the ones I had around. Be certainly will hold up to the outdoor elements for many years.
I can comment on pigments. I worked in an art museum, and did some painting years ago. I suppose the various mediums have improved over the years. What I offer is somewhat dated.
Most acrylics and oils use the same pigments, but the grade of the vehicle differs. If it says "student," the colors are often mixed w. a neutral powder, and so are not as vibrant. I'm not certain if different vehicles are used in acrylics, it used to be something called rhoplex, and the primary difference between different grades was the amount of the medium. Better practice was to buy more expensive tubes, and a jar of medium to be used for thinning as desired. Acrylic varnish can be used as a finish. There are special finish varnishes designed to be stripped away as the varnish surface absorbs dirt, etc from exposure, and then reapplied, leaving the original paint and varnish untouched.
I see that there are now artist oil paints that use alkyd as a vehicle. Assuming my recollection is correct, alkyd is made by heat treating linseed oil, the traditional medium, so that the paint dries to the touch in just a few hours, not days/weeks like linseed based paints. Probably would be a good choice, and I suppose it could be sealed w. polyurethane.
The labels of the tubes should have a light fastness rating. The American scale runs from 1 to 5, one being the best. The British scale runs from 8 to 1, 8 being the best. Most pigments used today are pretty stable. But sometimes the student grade paints are fugitive, and will fade within a few years.
