What you are looking for is most likely "Federal Standard 595". It has been a very long time... since I used it, but doubt if you can download the color samples themselves. Even in the old days (before internet) physical color chips had to be delivered to insure that everyone was referring to exactly the same color.
I just checked the ASSIST site. The document, FED-STD-595B COLORS USED IN GOVERNMENT PROCUREMENT hasn't changed since 1994 nor has the procedure for obtaining one since I last did so in 2002:
Establish a Commercial (non-gov't) account by applying at
Wait up to 5 days for a 'Shopping Wizard administrator' to review your application and send you a password via email.
Download & fill out the document request form
(either electronically or on printout).
FAX to DoDSSP Customer Service - FAX: 215-697-1462 or (215) 697-9398
Wait for hard copy by mail.
It's rather large; give it a separate 3-ring binder.
P.S. If you only download pdf files via ASSIST QuickSearch (w/o logging in), they try deleting your account about once a year 'to conserve system resources.'