No, most people have nipples that are darker(if only slightly) than the skin. This doesn't mean anything is wrong with you though. My friend's nipples are like that. Don't ask how I now :)
the nipple's are mostly pink or brown
Some nipples are differnt mainly because the color is varied in other parts of the skin. There is no problem with it.
Nipples become darker when pregnant
Her nipples are BLUE
Her skin tone.
how do rocks differ in shape hardness color texture
The rings around your nipples are what change in colour and are due to the changes in the hormones that your body is creating.
The distribution of pigment makes the skin tougher.
in some girls yes they are
darker hue then they normaly are