Good question john, and one that is absolutely fundamental to managing your gout.
Colchicine stops gout pain by fighting the inflammation caused by uric acid crystals. It does nothing to get rid of those crystals, which build-up as urate deposits in the skin and joints. Soon, the urate deposits start damaging bone, cartilage and ligaments. No amount of colchicine will help you once that has gone too far.
Allopurinol reduces the amount of uric acid in your blood, which stops new crystals forming, and helps dissolve old ones. It is vital that you carry on taking it every day, and make sure your uric acid levels never rise above 6mg/dL (0.35 mmol/L).