How come my item didn’t turn purple when I added the 4 mythstones? And the right ones.
Could you post a picture of the piece of gear and say what mythic you where trying to craft? 
If you put the mythic string on the wrong gear it won’t work. I did that once. If that is what happened, at least you can Garnet them off.
It is so easy to mess up and place a mythic on the wrong gear. I have done that plenty of times.
Especially when it’s 2:00am and u r hastily crafting that uber gear u been wanting 
this will help
try to check or review what mythic skill you want to craft.
ex. Cosmic Orb for Main hand weapon only can’t be crafted in chest(robe or leather),off hand,ring, amulet and helm(cap or hat). You must know the restriction in crafting mythic item/s.