I painted the softballs pink

[Fluid Fastpitch]

As we progressed working spins it became better for us (pitcher, catcher, Dad) to simply darken the seams on the balls she was practicing with. I believe this helped with the ultimate goal of being able to recognize her spin with regular game balls and make appropriate adjustments from seeing those seams/spins.

Yeah, I hope the kids outgrow the need, but right now my target audience is beginners who haven't learned to read spin yet.
Out of curiosity, did you use a fabric dye like Rit, or a leather dye?