How do I cosmetically resurface a bathtub to get rid of a greenish / pinkish hue?
I suspect the off color of green/pink may be from chlorine or fluoride added to the water supply.  Does any of the bathing soap products you use have green dye in them?

You didn't mention what your tub was made from. Porcelain  or fiberglass? In either case, I would try a product called CLR first. This is good for removing hard water stains.  The second product I would try is Barkeepers Friend.  This product has an ultra fine polishing compound and ascilic  acid, which does a great job removing scum, stains and restoring a shine to most any hard surface. It is safe to use on either material.