[jitter] Scalebias on GPU

Hi,
Forgive me if this is an easy question, but how can scalebias be performed on the GPU using a shader? I can see that a scalebias shader is already available but it doesn't offer any RGB control. Does it work in a different way or am I better using a different shader? Essentially I want to colour a white video different colours on the GPU.

Cheers 

Andy