What a great question Ace!

Finding colored Asscher  cut diamonds is very difficult.

This having to do with difficulty of extracting color.  The culture is limited because you can only play so many facets on the diamond.  A radiant cut allows many more facets on the diamond, which help the cutter to extract the maximum yellow color.

Still, we have had them over the years.
The next question involved a fancy gray greenish yellow... a very difficult question to answer as some diamonds with that color grade are very attractive, and others are hugely ugly..
If it was a very attractive diamond and really did have a green look to it, $100,000 would not be a lot.  On the other hand, if it was just a dull Gray, it might be $10,000.

A GIA graded "Fancy yellow" 3 carat Asscher cut, if it is a VS stone or better, could bring up to $60,000.  A radiant cut would be quite a bit less.

Your next question was about how the price jumps as you go from one carat size to the next.
Yes, the change is exponential.  That is to say, if a hypothetical one carat Asscher cut diamond in fancy yellow costs $10,000, and the equivalent 2 carat would likely be about 15,000 per carat, or $30,000 for the diamond.
In this hypothetical example a two carat diamond cost three times, what a one carat diamond does.