Have we had a gemstone drained of color by Awakening? Are there any WoBs about using the color of a gemstone to Awaken? Just because there's another non-pigment way to produce color doesn't change the fact that all the Awakening we've seen on screen was draining pigment from things.
I never said the pigment loss was a source of life threatening danger. I was merely pointing out another example of pigmentation loss around the use of Awakening. When non-sentient Awakened objects are created color is drained, when Lifeless are Awakened their color drains, and when Nightblood is drawn color is also drained. And interestingly enough, the flesh of Lifeless and Nightblood wielders are similar examples of losses of pigment. That's why I said, "dead flesh zombie color" to compare it to the affect Awakening has on Lifeless.
I believe that wielding Nightblood is an active form of Awakening. He is constantly trying to expend Investiture to destroy evil when he strikes things. He draws the Investiture to fuel this destruction from the user, but since this is Awakening, color is being drained in addition to the Investiture consumption. Obviously the Investiture draining component is what puts Vasher, Szeth and Lift at risk when wielding him.
I'm actually wondering if they're permanently gray-streaked. Vasher is never described as having streaks of gray on his arms, despite clearly suffering the same effect after wielding Nightblood. His Divine Breath may allow him to repair this damage if it is permanent. But I feel that in the amount of time that it takes natural skin cell replacement to occur, Szeth and Lift's bodies will replace the flesh that has lost it's pigment. However, if my theory is incorrect and the pigment loss is more permanent, they can probably use the healing powers of their Investiture.
I know the metals don't fuel Allomancy. I know that energy comes from Preservation. Unfortunately the definition of fuel is somewhat loose, and I'll use it when I mean to describe a reactant of a process. I was merely comparing something that is used up in the course of Allomancy to something that is used up in the course of Awakening. Even if they aren't the primary source of energy in either reaction, the fact that they're both required and subsequently consumed in the reaction makes one want to call them a fuel.
I think a lot of the magic systems get their kick start from the spiritual realm. Especially the genetically based ones that require you to be born with a connection to allow access to that jump starting process. Feruchemists have an inherited connection to Preservation and Ruin that allows them to access that Spirtual Realm power and begin the tapping or storing process. After it starts, the flow is completely between the Feruchemist and her metal mind. Likewise, I think a connection to Preservation allows for Scadrians to access Preservation and begin the metal flaring process.
However, Awakening works for anyone as soon as they have Breaths. Even if they aren't native to Nalthis. Awakening is Endowment's magic system, where do these foreigners get connection to Endowment's Investiture that allows them to perform an Awakenning command? The only commonality is the Breaths. Those Breaths are of Endowment. The Breaths themselves are the pathway to her power.
Please don't put words in my mouth.