Actually, there is a reason that many Mac owners describe the machine's case (often using color) when posting in computer forums.
In recent history -ever since the iMac- Apple has changed the design of their cases with every new revision to their desktop lines. Aside from being a good marketing tool, it also provides an easy way to tell models apart.
Perhaps the most striking difference between models is between the Beige G3 and the Blue G3. Although these machines share the same processor, the underlying architectures are fundamentally different. Blue G3 machines use what Apple calls the "New World" architecture, a layout now common to all of their computers, first pioneered in the iMac. Among other things, the size and role of the infamous Mac ROM is drastically reduced in New World, which was originally supposed to be a transitional design on the way to a totally ROM-less architecture, "Open World". Open World got killed by Steve Jobs along with the clones, but New World lived on. the reason New World is important is that the boot process is significantly more powerful, but also fundamentally different from, previous designs.
mrichich also notes the strawberry iMac, stating that it isn't possible to tell anything important about the machine from the color alone. Actually, this isn't true. "Strawberry" points to the third revision of the iMac line, which made some significant changes from its predecessor, but was in turn very different from the fourth revision, which included FireWire and a faster processor among other things. These are things that most iMac owners frankly neither know nor care about, and thus getting detailed technical information out of them can be difficult, but the color of the machine actually carries significant connotations in the Mac world.
By and large, of course, this phenomenon is unique to Macs. However, within that community, it is actually highly useful.