I have at least a half dozen or so interior design books for color. Although not cheap, I buy some really good quality, professional grade books, and the impression you leave does stand out. I try to educate them a little on color and what it will do for them from experience - large room/small room, emphasize mood, architecture, etc. For interior I will give them choices between BM Aura, SW Duration, American Pride, etc. in relation to what appearance they will have as far a sheen. I will state that it is just my "opinion" and tell them what they want to hear. They are not choosing an off white satin paint - they are choosing a suble tone with a hint of sheen that will make it very sophisticated and attractive. My main focus is to try to steer them to colors that would be easier or more workable for me. I also want a color(s) that will make my work look good when I am done.
I try to differentiate myself as the expert unlike one of the other contractor estimates that they recieve. The books help A LOT. I leave them when I do the initial measuring/estimate and pick them up when I go back with the price/sale.