I am currently Rank 10 in GTA 5 and I still cannot unlock crew sprays. Is it an in-game bug, or should I do something specific?
If you are referring to the crew paint job color for cars, you need to be level 20.
From IGN's Wiki on Crews:
- Level 20 - Able to set crew emblem decal, and color on cars
I believe that this is your Crew level, and not your character level.