Depends on where you go, in Eastern Europe they are very common but in America I would say they are rare. My eyes go from a bright blue to almost true grey. I would say they are a very recessive trait like brown eyes because only one grandfather had grey eyes and almost everyone in my family has or has had a little grey in their eyes at some point in their life.
The eyes will most likely be blue as the gene for blue eyes is dominant over the gene for grey eyes. However, there is the possibility that the mother has a recessive gene for grey eyes and in this instance the child would have grey eyes. However, it is morel likely that the child will have blue eyes.
Typically grey eyes are a version of blue eyes. Look closely at the grey and it's more greyish blue. I've got grey eyes, my mom has blue, and my dad has brown. My eyes were blue as a child but changed enough to now be clearly grey - pretty much smoke grey. But there is still a bluish undertone. It's just like hazel coming from brown or green... it's just a bit of a blend.
Green eyes aren't really special. Green eyes are rare, and most people find them very beautiful. Usually if someone has green eyes, one or both of their parents has blue eyes. Green eyes are some what annoying because they have trouble with sunlight. Some colors you can find mixed with green eyes: Brown/Green (like mine) Grey/Green Hazel/Green And sometimes, turquiose eyes can also happen.
Green eyes are more rare than blue eyes. Brown eyes are the dominant characteristic, so they're not rare at all. Green eyes are rare, because it tends to occur when a brown-eyed/green-eyed couple have a baby. Most of the time, that baby will have brown eyes (since brown eyes are dominant). However, sometimes, the baby can have green eyes.