This system has always confused me, I never owned one back in the day and it wasn't until I started playing Zelda DX on the 3DS this week that I even played a GBC game.

Can someone please answer the following?

1. Why are its sales counted as 'Game Boy' sales? Isn't it a new system all together? According to wikipedia it has a 8MHz processor compared to the original Game Boys 4.19MHz (faster than the SNES 3.58MHz wtf?) as well as various other improvements.

2. How the hell are some (the black carts) playable on original Game Boys? Zelda DX was one of these and it clearly displays more than 4 colours which is what the GB was capable of?

Some carts are only playable on the Colour, old GB games can sometimes use the SNES hardware in the Super Gameboy to display colours, Pokemon is an example of a game that uses the SNES to gain colour, uses the GBC to get colour, and is playable on the original GameBoy.

As for not being two separate systems, I don't know. Maybe there were a lot of GB games released even after the colour update?

The GameBoy Color is indeed the successor to the GameBoy and a separate system, but at the time, Nintendo didn't see a reason to bother with drawing a difference in the books. They still sold various versions of original GameBoys, and many games were still made compatible with original GameBoys.

As for the game compatibility, Nintendo designed the GBC's hardware similarly enough to the GameBoy's that many games could be created to be compatible with either. Plug it into a GBC, it reads that it's in a GBC and sends out a color signal. Plug it into a classic GB and it sends out the classic four-color black-and-white. It's... pretty simple.

1) Because they are basically the same system. The faster CPU was only used in a very small number of games. It was probably cheaper for Nintendo to go with the new CPU which is why they put it in there. Also the CPU could run at "normal" speed (same as Gameboy) or "2x" speed.

2) Again, they are basically the same system. The CPU could run faster but the Gameboy Color is still a Gameboy... in color. You could either play a game in black and white on an old Gameboy or play the same game in color on a GBC. Also, the Gameboy couldn't display 4 different colors, just 4 different shades of green (or grey, depending on the model).

Think of it as a DS and a DSi: The DSi has a faster CPU and more RAM but they are used to play the same games. You could, in theory, develop a game that requires the extra CPU power of the DSi but that would severely decrease the number of potential customers. The same was true with the GB and GBC which is why a lot of developers decided to make their games playable on both devices, the only difference being color.

Also, if I remember correctly, it was not "some" but "most" games that could be played on both models. The Wario Land games could, as well as the Pokemon games (all but the "Crystal" version) and even the "DX" games I think.

Gameboy Color should be considered another platform. Because not all GBC games are compatible with the original GB.

First - and only - handheld console I owned. Could play both Pokemon Red and Pokemon Gold on it. Good times.

Yeah, I think other people have answered your questions. It was a separate console, but kind of 'barely' a separate console :(

I see where you're coming from but I disagree here because in that case:

- The DSi was a seperate system because you couldn't play DSi games on a DS (Lite)

- All PSX systems sold with the original controller should be counted seperately because some games required dual analog input (and we don't know how many people upgraded to a Dual Shock just as we don't know how many people never played a GBC only game on their GBC)

- The PSP Go was a different system because not all PSP games could be played on it and it didn't have a UMD drive

By all means the GBC was probably somewhere inbetween a new system and a remodelling of the black and white Gameboy. And it's questionable which side it was closer to. So we're all right and wrong at the same time. Mindfuck

By that logic, the psp and psp go are different systems. There are plenty of psp games that the psp go can't play. If you own a go, you need to buy a regular psp as well to play these other games. The Japanese Wii and USA Wii are seperate systems. Plenty of games the japanese wii can play that the USA wii can't, so if you own a USA wii you also need to buy a japanese wii to play these games. I could go on... 

I get what you mean here but the Dual Shock was just an accessory, the original models could still play and PS1 game ever released.

That would be like saying the original 360 without the hard drives are seperate consoles as you couldnt download digital games, but again the hard drive is just an accessory.

With either of these you could simply buy the necessary accessory.

If however i wanted to play one of these:

Id NEED a GBC

Your criteria was that if you need a new console to play certain games it's a seperate system. And region locked consoles and the psp meet that criteria.
I understand my statement is silly, but that's just because your critiria was silly. If what you meant is that there are certain GBC games that the original gameboy is not capable of running due to hardware limitations, then it makes sense to exclude region locked systems.