For a healthy 36 year old, after gout attack has resolved, can colchicine (alone) be taken to prevent future attacks and how much and for how long?

Colchicine is rough! For the long term, Allopurinol is preferred for the prevention of gout attacks. Colchicine is a bit too powerful to be used in the long term. It has too many side effects.
No. You need to be on a med such as Allopurinol to normalize serum uric scid and prevent the long term complication of joint damage, kidney disease and stones and arteriosclerosis. Colchicine has no effect on uric acid levels. Btw, diet has little value.
For acute treatment. Only and not for prophylaxis. There are 2 other medications for prophylaxis ( Allopurinol and uloric) talk to your doctor about these medications.