So I have a GE water dispenser that has Hot, Cold and a 'Fridge'

So lately the watter is coming out either Green or Brown, (I'd have to ask
someone as I cant see the difference between the two colors)

The Water in the 5 gallon bottle is clear and looks clean. If I fill a few
glasses of water it comes clear. The unit is in my office, which usually
has the lights off and has never seen the light of day. So Its not algee
from the sun or anything.

1) What is it?
2) Why is it there?
3) what is the best way to get rid of it?

there is still about 3 gallons of water in the bottle. Any tricks for
getting the bottle off without making a mess?

Thanks,
Scott=-