As of 10.5.5 the only impacted chipsets are the Intel graphics adapters (X3100, and possibly the 950). The new MacBook has the 9400M which is a derivative of the 8600/8800 NVIDIA designs - the 10.5.5 driver for those has restored 256 color support.
We have a Diablo II patch in testing which can resolve this issue on the Intel chipsets, but I do not have an ETA for the release.
Good to know, and thanks for the heads-up about the patch! Looking forward to getting it; I'm very glad that Blizzard is taking an active interest in this issue. More developers need to learn from this example, and that's the plain truth.