Gamecube Not Displaying Color/Grayscale Only

I am trying to help a person in figuring out if his issues with the lack of color display is due to his GC dying or if it is the choice of the cables he has chosen to rectify the issue. Like him, I ggogled for an answer but have yet to find anything. Then it hit me that After Dawn has an active Gamecube forum. So if you guys have advice/fixes for this issue it will be much appreciated.

Here is what he wrote:

I am desperate and have googled everything I can think of with no results.

My gamecube won't read in color. Everything is grayscale. When I googled this, everyone seemed to concur that it was the cables, so I went out and bought a new cable with high hopes. Unfortunately, when I hooked it up to the TV with the new cable and turned it on, everything was still in grayscale! So there's something wrong with the cube itself.

Anyone have any ideas on how to fix this, whether it can be fixed at all, or if I can do it at home? I have never tried to repair a gaming console, but I don't want to just go buy another cube somewhere if I don't have to.

To be more specific, the cable I bought was a universal console RCA cable, not anything digital or RF or whatever. So it's not nintendo brand, but the original cables are hard to find since Nintendo doesn't make them anymore.