multipass mutliply

In my register combiner code I have two colours and multiply them together for my final result.

I want a multipass version so I use glmodulate with DST_COLOR and SRC_COLOR, but the result looks different.

What should I be doing to write a colour first pass and then 2nd pass multiply the new colour with the colour I wrote in the first pass?

I had to set src to ZERO and dst to SRC_COLOR.