Hi
Heres a full res. crop of an image I took with my 50mm f1.8 lens @f5, Modded 350D
because I carefully focused it wide open then stopped it down the star images were pin sharp, I was also guiding it as carefully as if I was shooting through the 300mm lens. See the scattered green stars. Real green stars dont exist, I believe whats happening here is that with a one shot colour chip images have to be blurred enough to fall across at least all 3 coloured pixels, and the antialiasing filter does that, however here some stars have fallen across just the green pixels only, and theres also a few purple stars too, perhaps they are white stars that fell on just red and blue pixels only.
I guess its rare a DSLR sensor has to cope with images too sharp for them to show true colours.
Note, modded DSLRs still have their antialiasing filters, its only the IR cut filter that is changed I believe
Scott