If you can note the lighter tinge, from the nickle, then you would still have to weigh it to be sure. The color alone, is not definite enough,(for me), to be sure. Weigh any you are not sure of. Copper-Nickel will weigh 4.67 gm,+/-, due to wear. Bronze will weigh 3.11 gms. Same exceptions. Hope this helps.
Dick