Looking good..
If you do not have any means of painting the poppers, you can buy rattle can spray paint and spray them. You can get some nice effects with this, but unfortunately, cannot do detailed jobs.
With the surfboard foam, I would suggest sealing it with epoxy/resin first and then painting as it is quite soft. I used to do this when making saltwater poppers for fly-fishing.
Here are some effects you can get with a normal rattle can spray paint.
Silver base coat, metallic blue back, and then pull a net over it for scaling effects..