Well, I am sure your approach will make it a bit easier to print from slightly scratched negatives. That is one of the main reasons a diffuser source is preferred over a condenser source. As for blue light: If you use VC paper, it will simply give you the highest contrast the paper is capable of. So you would have to use graded paper. Not in principle a problem, but then you can use any pure colour, and get into the part of the spectrum to which the paper is most sensitive. It might be that colour is blue, I don't really know. Green would be better for your eyes to work in. I would only do this if my enlarging lens was not very good. I don't have that problem, since I use Nikkors, Rodenstocks and Componons. They are all good enough that I don't have to bother with monochromatic light. Given the hassle of working with graded paper, a decent enlarging lens seems a cheaper and more efficient solution.