Hmmmmm. The Bondi Blue iMac? in aqua if I remember correctly. And the non-rainbow Apple (wrong order for the colors to be a true rainbow) was printed in spot colors and required six runs through the press in addition to any black print.
For normal printing on paper, like manuals and disk labels, they could use four-color printing. But for printing on other materials, like the logos on the computer case and the stickers they included with every computer, it had to be spot color. Not many presses could do six colors at once, and multiple passes are next to impossible.
The other major challenge is registration, getting the different colors to line up with each other. Gaps between colors are obvious, so most printing bleeds one color under the other for a tiny fraction of an inch. On the Apple logo, the bleeds are also pretty obvious; so it had very tight tolerances. The stickers were also die-cut, again with very tight tolerances.