One of the most important of the four Cs is color or lack their of, really. The Genologial Institute of America is established scale that begins at D and ends with Z to determine a diamond's color. So D, E, F range, any stone in that range is gonna be colorless. Then we move down to near colorless faint, very faint, so and so force, until you get down to Z where you can see a noticeable tint of color in the stones. When stones fall off the map, pass, then they become fancy colors. The fancy colors actually increase the value with their color. So basically, many of the color differences are subtle especially to the untrained eye but they do make a huge different when it comes to selecting a stone and price.
Most retailers carry diamonds that range from D to G, maybe D to I. So you have lots of options and different price ranges. If you have two stones you're comparing, one has better color grade than the other, it's definitely effect the price, but very important C to consider when making you purchase. So basically that's how to understand color in a diamond.