Nipples will darken during pregnancy.
Yes, and you might not have even noticed before you were pregnant, but there is actually a good bit of hair around the areola beforehand.
Yes; it is common to have sore nipples during the first trimester of your pregnancy.
No the nipples do not change colors.
The breasts and especially the areola and nipple of females can be very sensitive and give pleasure during arousal and coitus.
That is perfectly normal.
They grow into proper baby suckling nozzles. Until the first pregnancy, thick, prominant nipples would just be nuisance.
It does change in later stages of pregnancy. But not sure if it really starts in the first 2-4 weeks. - ASY
Yes they usually gets darker during pregnancy and breastfeeding.
You are not supposed to start producing milk during pregnancy. You can express little yellowish fluid from the nipples, during pregnancy.