My understanding is that it was a custom paint for Roush for the Premier Editions back then. It was one of 12 colors that Roush used from Plant Color (Sherwin Williams). If you want something close, Planet Color is where I'd start.
1998 Roush: M112'd Aluminum block 4.6L 2V 6 speed track car
1999 SVT: Mostly stockish
1970 Mach 1: Resto-modded monster
2000 Roush #5004 - World's FIRST M112'd V6 Mustang. Sold, but not forgotten.