US-FAA14 CFR 71.13
Classification of Air Traffic Service (ATS) routes
Read the official ruleOfficial FAA regulation text (public domain)
Unless otherwise specified, ATS routes are classified as follows: (a) In subpart A of this part: (1) Jet routes. (2) Area navigation (RNAV) routes. (b) In subpart E of this part: (1) VOR Federal airways. (2) Colored Federal airways. (i) Green Federal airways. (ii) Amber Federal airways. (iii) Red Federal airways. (iv) Blue Federal airways. (3) Area navigation (RNAV) routes.
Verbatim text of a US Federal Aviation Regulation (public domain), reproduced for reference — not legal advice and not for navigation. A plain-English explainer may be added later; always rely on the current official rule linked above.