Ok, from what I had read, spiders and pins are both dominate but only contain one gene for their trait, so that they can pass on the normal gene, and make normal babies with normal partners. Is this true?

I was talking to a friend and he thought that all pins produce 100% pins when bred to normals.

This is what gets confusing to me.... if spiders and pins are both dominate forms, when you breed them to other spiders/pins and produce offspring, couldnt some of the babies look like spiders and pins, but have the genetics to produce 100% when bred to a normal?

I know it would be hard to prove without breeding a lot, but just curious.