Gold. Donahue reproductions has it I believe. I have also found out that the gold for Oldsmobile engines you can find in the auto parts stores is really close if you are not too picky on being perfect.
Uh, sorry, but Greg Donahue only has it partially right (at least the last time I looked in his catalog). The 390-4v/300 hp air cleaners/valve covers on T-birds and full-size Fords used Castillian Gold, Ford color M-1459, which was also an exterior paint color, code "I" in 1962-1963. The gold that typically is passed off by parts vendors, which was used on small-block '64-'65s like 298 Mustangs is too bronze. The Oldsmobile gold also falls in the "too bronze" category. The gold color used in 1960-1963 for hipo 352s-390-406s is Gold Bronze, Ford color M-842 - it is a more-golden/bronze color, but it is NOT the correct color for '63-'64 390-4v/300 hp engines. If you're looking at old Ditzler/PPG paint charts, Castillian Gold is color number 32277, while Gold Bronze is #21903.
T-bird parts vendors do get this wrong - a LOT. One vendor I know has a spray-bomb formulation for Castillian Gold that I've used which is mixed correctly - The Bird Nest in Portland, Oregon.