I have tile already in place around a fireplace. It is smooth, well placed tile, however the color is terrible. Should I break this tile up and remove it or tile over the top of it? Thanks.
Breaking the tiles could be a bit messy. You may end up pulling a lot with them, although you can always re-plaster the damage.
Normally you can just tile over existing tiles. If the tiles are too smooth score them with something sharp. Depending on the fireplace (not knowing what yours looks like) you'll have to be carefull that overtiling wouldn't protrude too much and that you could spoil the look by the overall thickness.
Personally i would take the existing tiles off, but then i would be prepared to smooth the wall/backing of the fireplace. Depends how confident with your skills you are.