as usual with this threads, this can be common knowledge and i can be the last player in the game that discovered this trick. however, i fell to post it.
so, you have two weapons equipped. one is legendary. you draw it and swap weapon. from inventory, double click to equip another weapon. this new weapon should have the aura of the legendary you have equipped. if you double click the other weapon from inventory, the wave of colors (sunrise here, dont know about others) will appear.
it wont change your game, but think about two whisperblade with the purple aura of quip or something like that, you can do cool combinations even if you only want to do some screens!