color matrix and tangent space

I am doing dot3 bump mapping by encoding the tangent-space light vector in the vertex color. If my object moves, can I
use the color matrix to transform the light vectors? Or can the resulting light vector
be unusable for dot3?

As far as I know, the colour matrix is part of the imaging subset, which isn’t supported on most hardware.
Anyway, you’d have to range uncompress/compress it too, which I don’t think would be possible with the colour matrix alone.
You should use a vertex program to transform your light vectors in the colour stream. That is the solution.