I havent gotten behind the console, but thats like, exactly what I was gonna do, except precompute like 5 or 6 tween values for r,g,b between 255 and the target for greyscale.

But rather than do that and cache them for timing triggers, I kind of like the scaling down by multiplication approach.

Edit: manipulate the rgb values that is - I wouldnt have converged on those hard values on my own.