I was going to mention the DMG thing that Revend already did...
Technically these aren't acronyms...I believe acronyms are supposed to spell something, and "GB" by itself isn't a word.
Then there's "GCN", the official abbreviation for the GameCube. Everyone thought "NGC" meant Neo-Geo Color but that's because they're not familiar with the Neo-Geo line...the Neo-Geo is obviously in colour and the Neo-Geo Pocket Color would be "NGPC".
Then there's the PlayStation, which seemed to be PSX, but then they released a Japan-only PS2 with extra media functions called the PSX. There's the PSOne but I think that should refer only to the redesign, and by extension, some people call the PS2 Slim the PSTwo. I remember someone calling the PS2 the SP2 because she thought the S stood for "Sony" and P the whole "PlayStation". I avoid calling the original the PS1 since the "1" is kind of a backwards term, like naming movies with a "1" (except in obvious cases like Loaded Weapon 1 or whatever that Lethal Weapon paroday was called). Then again we all refer to Transformers as Generation 1 even though it wasn't at the time...
I don't see a point to call the Game Boy the Game Boy Monochrome. Does monochrome mean black-and-white or does it include shades of grey? And the original design didn't really look black-and-white, really. The Game Boy Pocket was closer to it, but the original was more like shades of green, wasn't it?
In context it's easy to tell if you mean the original Game Boy specifically or if you mean the whole Game Boy line of handhelds in general.