How Come Original Game Boy Games Have color on the later handhelds?

The Original game boy games were all like Grey scale, right? But ive got a few old Game boy games but play them on a Game boy advance sp, where they have color... how did they know to put color in these games when they were made to be seen in black and white and gray?How Come Original Game Boy Games Have color on the later handhelds?I think the games itself had color already (but barely any difference, like Pokemon Red [which I own] is just all red) but the actual old Gameboy could only display in black and white. But the new Gameboys display in color. I owned an original Gameboy too for awhile and I remember playing Warioland (which was for the Gameboy Color) on the old Gameboy and it was black and white. So yeah I think its just the way the screen it displays.How Come Original Game Boy Games Have color on the later handhelds?Probably just a chip in the GBA that reacts with the original GB games making them color.How Come Original Game Boy Games Have color on the later handhelds?because they were made for GameBoy color....