Not directly tied to an answer, but as food for thought, Tenbones' description brought to mind Lois McMaster Bujold's more recent works (the Penric books/novellas) where the magic system is tied to the amount of chaos intrinsically applied in its use; she describes "Upstream" (or was it Uphill?) magic as magic that moves towards Order (healing, repairing, creating) while "Downstream" magic is injecting chaos into an action (destroying, heating, etc). Uphill magic is a LOT harder to do, and in the setting the caster has to absorb the chaos into himself, then dissipate it later to restore himself to a balance.
I could see that in what you've described as a sort of balancing act, with Corruption replacing Chaos in the equation. A "White" sorcerer would never use corruptive magic, their effects are all tied to healing, repairing, and ordering of things. Used in their methodology, they have a "Casting Difficulty" of x2, and a "Corruption Mod" of x0. A "Black" sorcerer would never use White magic, and their effects will all be focused on destruction, disordering, etc. They would have a "Casting Difficulty" of x0.5 and a "Corruption Mod" of x1. A "Grey" sorcerer might sit permanently in the middle (Diff x1, Corr x0.5), or be able to use "Pure" effects on a sliding scale depending on what Difficulty they were willing to accept. ("Quicker, easier, more seductive, the Dark Side is...")
All of that was sort of to frame that I think the Effects should be the deciding factor of the White/Gray/Black scale, not the specific spell. While a Black Sorcerer might throw a Fire Bolt, a White Sorcerer might prefer a Cold-based spell with the same damage degree, simply because frozen things are more ordered than heated ones. While a White Healer might just use golden light to heal, the Black Priest may perform a blood sacrifice (causing a death) to cause someone to be healed of damage (with the death there's more corruption/evil/chaos in the world, so it's a win for that side..) I think you could get away with giving the entire list to all grades of magic, and then tailoring the effects to match the particular style of the caster.