[Danny-E 33]

It depends on the emulator you're using. I'm no expert in emulators and I don't know specifics about every kind out there. But I know bgb and Lameboy will display in color. I know Meboy cannot display in color.
If you're using VBA, its default setting won't disply in color but you can go to Options->Gameboy->SGB and that will allow all gen I ROMs to play in color.