1) Water which has changed color (by being mixed with ink or another colored liquid), is unfit for washing one’s hands, just like the water of the Kiyor (washbasin) in the Beis HaMikdash, which became unfit if it’s color changed. (Shulchan Aruch and Mishne Berura 160)
2) If the color of the water changed by itself, for example if it stood in a bowl until it turned green, there are Poskim who say it is unfit (Shulchan Aruch, Ben Ish Chai and Kaf HaChaim), and there are Poskim who permit it (Taz, Gr”a and Mishne Berura). Even according to those who forbid it, if one has no other water one should wash one’s hands with this water but should not make a Berachah.
