At the World of Concrete, Troy Vancil gave me a sample of concrete he had mixed and polished using a mix that was 50% fly ash with 50% pea gravel. It has a nice brownish green color with no integral color added. Troy added a few comments on recent projects using this approach:

Even a 30% fly ash mix is still a nice color, just more of a tan than brown. The projects I have done this with are a bar top and a gateway sign for a golf course development. I am currently talking to a franchise owner for a restaurant about doing the floor with fly ash instead of integral color. Is there a point of too much fly ash in a mix? I think 50% would look awesome but the architect is wary about anything over 20%.

I don't think I would ever need to try for 70% fly ash, the difference between 30% and 50% is not that great. I have attached two pictures for you to give you an idea where I am coming from. The first picture is of a house remodel that I did in 2009 that the client wanted a polished concrete floor with more of an earthy tone to it. To get the creamy color we used white portland and Increte integral color. The added cost of the two totaled around $2,000 for the slab that was 12x36 feet. Creamy almond type colors can be some of the most difficult to achieve using integral colors, usually 5 to 6 pounds of color per sack of cement.

The second picture is a floor I did in 2011 for a spa pedicure area where I used 15% fly ash in the mix with no integral color or white portland. The colors are fairly close (hard to tell in these pics but they are real close) with no added cost. I guess the point I was trying to make by giving you the sample is that contractors can give their clients a polished floor with more earthy tones by using fly ash and saving money on integral colors. Everyone I first meet and start a conversation on polished concrete has a preconceived notion of blah looking grays for a finished product. Schools already have an institutional look to start with. Fly ash could help get their floors into the warmer color schemes with no added cost. I am always trying to be sustainable where I can, and I hope fly ash can help out in the future not just from a reduced cement content but color as well.