Colored golds

Yeah, I don't really understand that graph/diagram/visualization.

I was looking around on the web about the various alloys of gold that can produce different colors and happened upon that diagram up there.

So, here's my question, how do I read the graph?

Like, let's say I wanted to make a gold that would be as yellow as the Y in the word yellowish on that diagram.

My reading of that alloy is that it would be about 55% silver,  50% copper, and about 50% gold.

That math doesn't seem to add up.

Can anybody tell me how to read this graph?

Sure, there's a bunch of info on the Colored Gold wikipedia page, but nothing there is terribly helpful either.