What is the law or regulation which provides guidance on which color of money (i.e., 3400, 3600, 3010, etc.) to use for which purpose?
While the term "Color of Money" is a term of art and not a specific legal or contracting term, the requirement to use different appropriation accounts originates wth and is codified in Title 31 of the United States Code, section 1514 (31 U.S.C. §1514) (Federal Law), and is further delineated for the Department of Defense in DoD 7000.14R, Volume 2a, paragraph 010107 B. This is further delineated by your service branch in AFPD 65-6, AF Manual 65-605, volume I, and AFI65-601, volume I, dated 24 Oct 2018. Please ensure to check to see if your command, wing, or unit have added further clarifications that might be relative to your request.