Couple facts...
Evolutions is estimated to be about 200 pages. I may still be WAY off on this figure. I am also one that would lean for a cheaper book, especially considering that most of the art is B+W anyway.
When the D20 Amethyst was released in 2008, it was primarily softcover with a limited run in hardcover. We discovered that despite the cost difference, customer always wanted a hardcover.
With Evolution, printing options are for hardcover color or B+W...or so we initially thought. I just recently discovered that the printer won't be offering a color hardcover, meaning we are limited to B+W hardcover or color softcover...and that's not much of a choice. I think given those choices, you guys would all want the hardcover, especially for a large supplement like Evolution.
So in the end, this could all be moot...

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“I despise stallions. I ride them as I ride an ugly noble women--smiles for appearances and politics only. Stallions. All personality with no depth. They prance like ponies and trot with arrogance. I always say, respect your mules most of all. A stallion may lead with the king and gather the eyes, but a mule will follow behind…and carry your kingdom.â€
Tsarevick Kazaan
Amethyst D20
http://www.diasexmachina.com