Weapon Battlepacks are Black
There's Bronze, Silver, Gold and Black.
You seem to get a bronze one every few levels or so, then a gold once you reach a certain milestone like Level 10.
I might be wrong but I think at a certain level you start getting silver's instead of bronze.
On a seperate note, I didn't realise you had to activate XP boosts you received in battlepacks.
I activated a 200% boost during a game of Rush and the boost lasted a whole hour, during which time I picked up a Service Star for Support, an Ammo Medal and a Service Star for the MG4. Probably went up three levels in one match.