WA-8631 is the pearl Diamond White paint used on the 1989 20th Anniversary Turbo Trans Am, Pontiac's collaboration with PAS (Pontiac Automotive Specialties — Mecham Racing) that swapped the standard Trans Am's L98 5.7L TPI engine for a turbocharged version of Buick's 3.8L V6 (the same engine family as the 1987 GNX). All 1,555 TTAs built carried this color in combination with tan leather interior — Pontiac offered no other configuration. The order code combination Y82 + B2K + WA-8631 on a 1989 fender / SPID label is the canonical TTA signature.
Diamond White is a pearlescent finish rather than a flat solid — a base color with a pearl-coat layer that lifts the white into a luminous off-white in direct sun. The pearl coat shows up as a subtle color shift across the body curves on the surviving cars. TurboTransAm.com is the deep-reference site for the 20th Anniversary cars, including original PAS production records and individual VIN provenance for many of the 1,555.