In the first photo - it looks brown, with some grey in it, and in the other two photos below the first one you can see yellow in it. My guess is that it is yellowish brown or brown yellow, very hard to tell. As for size, does the seller give measurements - that would help to give you a better idea if the stone is cut deep and faces up smaller. You might want this thread moved into Rocky Talky or Colored stones to get more responses. Also, since it is a colored diamond, to be sure it is natural and untreated, I would prefer a GIA report. I assume at the price point you posted that this ring probably does not come with one, so then I would want to be sure I'm buying from s reputable seller, etc with a return policy. Is the ring gold? I don't see stamp mark on it, so hard to say anything about the price as well.
Looks brown to me.
Is it treated? If it is, I'd pass. Also, what is it set in? White gold? As far as cut is concerned, I don't think that's something that can be determined from the photos provided.
The stone is set in 14k white gold, It is claimed to be a .75 carat princess cut champagne diamond
The seller is just a regular garage sale type guy, not a diamond vendor or seller
It's really hard to tell, because the color in the photos is so different from each other. I would try to find out from the seller whether the diamond is treated in any way, and if there are no red flags, as long as you like the color of the stone it seems like a reasonable price. For me, I would want to see it in person before I purchased.