Displays only black and white when turned on.

It sounds to me like there's problem with a pin in the display connector port on the SNES itself. If you've had it in storage, the copper connector may have oxidized, which will put a green-ish coating on it (like the Statue of Liberty). This will disrupt connectivity between the connector and the cable. This doesn't happen often under normal conditions, as the contacts are treated to resist oxidation, but long-term storage in a non-climate-controlled location can still cause such issues.

If this is the case, the contact may be cleanable, but you'll have to be careful not to damage it. There isn't a suitable guide for this part of the system yet and my own SNES is still in storage.

It's also possible the connector port was damaged. I find this less likely, but you should be able to tell by looking at it.

Take a closer look and let me know what you find.