One of the serger books that I ultimately bought after getting it from the library several times talked about getting colors that blend with what you sew. I seldom sew on white fabric or white backgrounds. They suggested a sort of dark rose/mauve tone, a grey and a dark navy as working with most fabrics. If you're sewing the seams and worry about show you can just use regular thread in the needles on that garment.
Some people are fanatic about an exact match of thread to fabric. I have been known to intentionally use something that contrasts. With the serger I might sew a black garment with black in the needles and red or gold in the loopers.
I have about 6-8 sets of thread and several are unopened, like white. Mostly I've used black, red, medium grey and a cream/off white on really light fabric, as those are what best suit my fabric colors.