re: Sun vertical
If what you said were the case, the outer part of the rim facing us would be white, and the inner part of the far side of the crater would be white. It looks like the outer part is bright all the way around.
Hopefully, detailed MGS photos of this area in the near future will clear a lot of this up.
As someone else pointed out, the brightness around the parachute shadow seems to indicate either a haze, or a "retroreflective" characteristic of the soil, similar to that of the Moon.