When I set my vertex color in my glsl vertex shader like this, it doesn't do what I expect. Specifically I expect that setting the alpha to 0 would cause the vertex to be transparent. But it isn't. The color stays there pretty visibly, and seems to get lighter. Why is that? Are they supposed to be pre-multiplied or something, where the following color might be illegal?

colorVarying = vec4(0.3,0.1,0.75, 0.0);