I have sales brochures from 1973, 1983, 1987, 1988, and 1989. The '73, '87, and '89 brochures most definitely have the rocker panels black. The '83 picture is a shade dark to be positive, but looks black also. The '88 picture is from a bad angle.
Not a single one of the brochures shows an example of two-tone paint.
My '88 is black, which seems to be the only way the rocker panels are body colored.
