Cris's Art Glass House

I've been experimenting with creating stain glass art. And I tried what I thought was white paint, which would add a nice pearl look. But it turned out that it really was white-colored paint that dried crystal clear. So it didn't add any color at all to the glass!

I went to the store and found actual white. But my question to you is simple. Why would anybody want to use clear paint that doesn't add any color at all?

The only reason I can think of is to add a barrier between two different colors. For example, putting on a layer of blue, then covering it with the crystal clear before adding say yellow to make green. But I've put one color right on top of another to mix the two together without anything in between and it worked just fine. So maybe there's another reason.

So I'm just curious as to what purpose having something that adds no color be when it comes to making stain glass pieces. Thanks everyone for your help!