That SGI board has the gray granite case. It's not that yellowed. But a rubber dome.
That looks like the white version to me.
I have seen both the older Dell shaped one and the smaller rubber dome one in both granite and white.
I think it is Yellowed so much its almost green!
Some of the sellers do seem to be asking ridiculous money.
But then when something is a collectable/antique then it is worth whatever someone is willing to pay for it.
(it does piss you off though seeing those prices)