Colors in the artist’s work don’t really refer to actual abilities in the card- if anything it will be a Metalcraft ability, which symbolizes Mirrodin as a whole. Metalcraft- Indestructible is HIGHLY unlikely, but I can see this-
Metalcraft- Flying and First Strike
Well, I’m going to have to fully disagree with you when you say prominent colors in the art ≠ abilities and/or color identity.
The example you used, Etched Champion, doesn’t make any sense. His ability it to have protection from ALL COLORS, and obviously there’s a rainbow of art on the card. More examples: 1, 2, 3, 4
The most common complaint about art that I’ve heard recently is that everything is styled the same and looks the same, that’s because art direction at Wizards is serious business now and there are obviously stricter guidelines now. And I guarantee you color identity is near the top.
Also, you guys both made mock metalcraft angel and I figured third one would be the turd cherry on top of your ideas—So I went wacky/something I’d like to see, disregarding most things. Obviously when they show art off early, it’s something they want to represent the set, and neglecting their set mechanics isn’t something they do.