You can get external video through the SCSI port for colour and some CPU upgrades. To quote LEM regarding the Macintosh Classic:

Accelerators

MicroMac Multispeed (16, 25, or 32 MHz 68030), optional 32 MHz 68882 FPU

MicroMac Performer (16 MHz 68030), optional 25 MHz 68882 FPU

MicroMac Performer Pro (32 MHz 68030), 64 KB cache, optional 32 MHz 68882 FPU

Discontinued accelerators (68030 unless otherwise noted) include the Applied Engineering TransWarp (16, 40 MHz), Dove Marathon Racer (16 MHz), Mobius (25 MHz), and Total Systems Gemini Ultra (33, 50 MHz).