Have you ever painted the plastic trim around a window on an steel exterior door?

You want to use 100% Acrylic paint.

If the trim is glossy, you'll want to scuff it up with some sandpaper first or use a primer so the paint will stick better.

You also want to stay with the lighter colors.

In direct sunlight, darker colors will absorb the heat and might warp the plastic.

Yes, Krylon makes a plastic spray paint. First lightly sand the plastic. Then, follow the directions on the paint can to make the paint stick. Usually, wipe it down with Mineral Spirits or acetone. Tape and mask both sides of the plastic so that only the plastic is visible. Take your time and you will be pleased with your results. If the door is facing the sun you will probably have to do this every other year or so.