Thanks for the reply.
I had read an article that claimed you no longer needed to colourise negs in this day and age. I did not know that the colour determined the density of the neg. Confused my poor weak brain!
I have done a bit of digging and have a starting point. I will use green (r25, g50, b0) and have a curve. The curve is for a different printer, but it's a start. (Long live film:-))