Yeah, trusting soil color alone is rough. I've seen fresh cuts look totally different under work lights versus sunlight. You really need that physical proof like tool marks.
Hold up, you were at the Cedar Creek dig in 1998? That's ancient history for real. But yeah, just going by soil color is asking for trouble in those mixed spots. Artifact wear or tool marks are way more reliable like you said. I got fooled once by a weird stain that looked like a layer break. Now I always look for those physical signs too.