Chris, either blue or white or bluish white. If you're burning coolant, the exhaust will have a sort of sweet smell and your cooling system will show signs of over pressure once the engine is warm. You can check this by removing the cap on the expansion tank, watch the level and observe for bubbles. Also look for oil in the coolant (head gasket). Oil burning can be either bluish white or white, depending on the amount burned. In either case, i.e. valves or head gasket, the head will have to come off. It cost me $865 for parts and machine shop when I did mine (blown head gasket, warped head), but I did all of the teardown and refit myself. If you're up to it this is the way to go, however, this is not a job for someone new to DIY. Ask Benzmac (Donnie), he was a great help when I did mine...
1987 BMW 325