i am 25 weeks & 3 days pregnant & my nipples haven't changed much in color, however, they have grown in size! i asked my mother about nipple changes, because she has 5 children & experienced it all during her pregnancies, & she said that it is different for every woman, as is expected. we all have different bodies, therefore it only makes sense that we deal with our pregnancies in different ways.

my nipples also started leaking fluids early on at around week 19 or so. also normal.
research it online & in books a little if you're that interested.