Color for SAN (Styrene Acrylonitrile)

I am familiar with two ways this is done.

In most cases the transparent material is changes to translucent by surface texture. If your material is rolled there are rough surfaces applied to the rollers that do this. Think if a clear plastic shower curtain that has translucent fishies on it. The rollers are etched similar to printing rollers. Thicker materials can be chemically etched like HF acid on glass.

A different method is to add a different material that is also clear but has a different refractive index. The combination diffuses light resulting in translucency.

You could add gray dirt.

Give more details of the method of mfg or intent, end product, you will get better answers.