Also, does one have the same required DoF roll if the skill involved is gray? It doesn’t make sense but it does say that the skill is used in place of strength.
No, you use the shade of the weapon. If you have gray power, gray Sword, precision training and even a magical spirit blade (black shade), the IMS is black.
Sure it’s the weapon’s shade that determines the damage, but the rules also state that if you have grey power you add 2 to the IMS, so that still applies. The shade of the skill never comes into it, however.
So the final outcome is [weapon shade] [skill exponent + weapon power +2 if Pow is grey]