The colour type has no impact on damage out put unless there is a modifier on the strike/raid i.e nightfall has a solar modifier on so you will do increased damage with solar weapons but the enemies with solar weapons do more damage to you. It also plays a general role of taking out sheilds, minatour have purple sheild so use void damage to lower sheild quicker, fallen captain has an arc sheild so use arc damage to lower his sheild quicker and finaly the wizards have a solar sheild so use a solar weapon to drop the sheild quicker. Why is the sheild so important?, when the enemys sheild is up no matter if you hit them in the head they will only take a set amount of damage so no criticals can be done, also your damage is reduced against the sheild unless it is the right eliment match. After the sheild has droped any type of weapon can hurt them, youll notice if you use the wrong weapon on a sheilded foe it will say 'immune' this is becaude you arent using the right eliment to lower the sheild and are doing lower damage.