Re: Authorized color for bags
Consult AR670-1 and post CG guidelines for adendums to said Reg. Also, this a question for your NCO support channel i.e. Your fireteam leader or your Squadleader. If you are wanting to use a nonissued pack while deployed or in the field, you are subject to uniformity if your CO, 1SG, PSG have an issue with it. Their issue would be related to enemy targeting of those who stick out.
This is a rather PV1 question. SPC and above should know the answer or where to find it.