Boss challenge reward

[Cawince_XBL]

Hello,
Sometimes, you can get a gift during a boss challenge. I have already seen 3 colors (grey, black and red) but the pack was still the same regardless of color and difficulty (common equipment).
Does the color mean anything ?
Does the difficulty matter on the reward ?
Thanks for your reply.
PS : sorry for my English, french player

[Cawince_XBL]

Up. Nobody knows ? Ty

[Djacks4_XBL]

Yea, this. Anyone know?