The yellow color applied to postwar trainers actually predated the FS595 system, which -- though it 'officially' came into use starting roughly 1956-57 -- didn't completely replace the old ANA standards until about 1970; that color was the old ANA 614 Orange Yellow.
The FS equivalent seems to be FS 13538, variously called 'chromate yellow,' 'Air Force Dark Yellow' or 'orange yellow' (among others...since FS colors have no official names, just numbers).
It's really more a true yellow with a distinctive orange tone. There are color photos aplenty online -- but note that it's a color whose visual appearance (especially the strength of the orange cast) can vary quite a bit given different lighting and overcast conditions. (Various hobby paint lines purport to offer the color...but their versions range from yellow to orange to a sort of brownish tone.) Always best to go by photos if you've got 'em.
Last time I mixed it for Monogram's 1/48 kit as a 1956 USNR SNJ-5, I just used Tamiya yellow and mixed in a little orange by eye to match the reference photos I was using, and it looked fine. The pics are still up on Instagram if you're curious:
https://www.instagram.com/p/CVdHi3rgWO-/?igshid=MzRlODBiNWFlZA==
Cheers