The GBC uses a Sharp CPU similar to a Z80, but not quite the same. The one in the GBC is extremely fast. So fast, in fact, that once Windows finishes booting, we'll still have time to get drinks and salads and Milliways before the Big Show.

There is a hashtable of GameBoy Mono games which are recognized by the GameBoy Color, and it applies a preset color scheme that Nintendo chose to make the game stand out better. Metroid II is a perfect example of this coloring. All of these GBC colored B&W games are run in plain B&W mode, even if they have Super GameBoy features, as the GBC is not a Super GameBoy and doesn't have the same features. There is a disassembled source file to the GBC Boot ROM linked on the dumper's website, with most of it commented and disassembled. (Except the game recognition hashing part, which is still being analyzed)

The gameboy color decapping attempts in 2005 (after the mono was successfully decapped) was a failure because the decapping was done by a student with little experience. I sacrificed a couple gbc units for that effort and one unit for a professional decap/bit stain which cost too much so it never happened. This glitching hack was discussed for many years before someone got the right idea.
This RE effort has rewarded us with info about hidden hardware registers that only the boot ROM uses.

There is a mod that can allow a GB access to an IDE device such as a hard drive, so technically, yes, it could run Win 7 in a super-slow-as-fuck emulation. For those of you who actually would like to KNOW what the boot ROM does, there is a link ON THE PAGE to a work-in-progress commented disassembly of the entire ROM, as has been previously been done with the GameBoy Mono and Super GameBoy.