geometryAttribute alpha color is unavailable

1. A concise explanation of the problem you’re experiencing.

I set color user geometryAttribute, the color is with alpha(rgba), but in fact, the geometry is pure, I watch the document, it says "The color attribute.

8-bit unsigned integer. 4 components per attribute." is alpha also an integer

2. A minimal code example. If you’ve found a bug, this helps us reproduce and repair it.

3. Context. Why do you need to do this? We might know a better way to accomplish your goal.

4. The Cesium version you’re using, your operating system and browser.

Can you post some sample code from your application to give me some context on what you’re trying to do? Ideally if you can provide a Sandcastle example ( that I can run that’d help me a lot.