[Oscar in Bin (John)]

Pete,
I use CCDStack and that has a nice simple gadient removal feature. However, I was having problems with colours when I combined RGB images - for example bad coloured halos. On investigation I found that I had negative ADU values after dark subtraction and prior to combining the three channels. Using pixel maths to get rid of the negative values by adding a positive floor worked very well in getting back to sensible colours.
John