I actually I am not sure Krylon makes a plastic primer. Krylon Fusion comes in a bunch of colors and is self-priming though. It is only availed in rattle cans. I have used it on outdoor furniture and kids play equipment. It seems to have held up although I did not go back to check on it. I found this Fusion color chart online but cannot tell how current it is.
Rustoleum also makes a plastic paint that is self-priming in rattle cans but in fewer colors than Fusion. I think BJ remembers me mentioning they also make a plastic primer that comes in both rattle cans and liquid form. They claim you can put any finish coat over it. I've honestly never used it but Rustoleum is usual pretty honest about product claims. I guess if you could not find a Fusion color you liked, or were trying to match something specifically the primer would come in handy.
Remember with rattle cans you want to apply several thin even coats rather than trying to cover your surface in one or two. And of course especially with plastic, your surface prep is critical. Make sure it is clean and scruff it up a bit to improve adhesion---even if using a plastic primer or paint.