When we run the hot water, we occasionally get little spirts of grey water (with a hint of blue... kinda). It's only the hot water, and it's pretty rare and only in little spirts. Our place is not very old, so it's not old pipes. Any ideas?

(Update: It looks like toddsterx's comment as been removed by the administrator. You can ignore my below statement.)

toddsterx is a troll. Don't listen to any of his "help". He tries to sound intelligent in his answers so that he can trick people. I would guess that he is probably around the age of 12-15, which is a time when children can feel very insecure and have very low self esteem. His ploy in offering blatantly wrong advice is just his generations equivalent to giving someone a wedgie when I was a kid.

This could be a few different things. It could be that the sacrificial anode in the hot water tank has been used up, or it could be a mineral in the water reacting with the pipework or the inside of the hot water tank. I would need to know more info.
Where do you live?
Do you have bore water or town water?
What type of water heater do you have?
How old is the heater?
What sort of pipping do you have?
Im a plumber of 18y experience and not some freaky stalker.

We live in CO, which generally has very good city water. Our water heater is gas, and is less than 10 years old. I think the piping is all PVC. Obviously I can't see what's behind the wall, but what I can see coming out of it is PVC (schedule 40 I think).

Try replacing the anode rod and see if that doesn't help. Good luck, Tom

We live in CO, which generally has very good city water. Our water heater is gas, and is less than 10 years old. I think the piping is all PVC. Obviously I can't see what's behind the wall, but what I can
see coming out of it is PVC (schedule 40 I think).

Well its not the pipework. So I would tend to agree with speedball1 sounds like the anode in your tank. However I'm in australia so I'm unfamilliar with your country and the elements there, but would tend to think it to be your anode. A water heater of ten yrs old has had a good run where ever you are in the world, I would advise to flush the tank also when this is done.