Kid...completely playing devil's advocate here in my response that pigment DOES make a difference:
You are correct about not being able to choose ball color unless it is entry level (Tropicals, Strike Kings, etc)...what about a ball like the Optimus Solid. I have one and have seen others punched and on display and the ball is a mix of red/yellow/blue (as stated on the box label). What if one Optimus comes out almost completely red...and another is almost all blue? Yes, they might be marked as 2nds or X Comps or whatever Storm labels them, but from ball to ball, there could be a substantial difference in ball reaction and as a customer, we have NO say in what ball we get. The red Optimus could hook X more than an almost all blue Optimus.
What are we going to ask our pro shop owner to do? Call Ace Mitchell (distributor) and have one of the pullers in the warehouse look through 10-15 Optimus Solids to see which one has more red pigment than another?