This is probably the best bet for figuring out the laws.
This one from the CBI list the statues that you need to know.
In a nutshell, you can OC everywhere except Denver City/County. You can OC/CC in your car without a permit, and you can CC while hunting without a permit. Watch out for "Denver Mountain Parks" because they are the property of the City & County of Denver, and prohibit OC as well.
Where in Grand County are you? Winterpark/Fraser/Tabernash area? Granby/Grand Lake? Hot Sulpher Springs/Parshall, or Kremmling?