I agree that blue smoke can definitely look white especially if the leak isn't too bad. You may want to (careful not to burn yourself) put your hand behind the tailpipe and see if you're getting a lot of moisture blow out, or oil blowing out. This will work if you're getting a lot of smoke. Another good sign of rings going is a lot of oily smoke coming from the blow-by tube in the back of the engine. The rings may be letting compressed air back into the crank case, and letting oil up into the cylinder.