Color refers to the body color of the diamond. Fancy color diamonds aside, the best, most beautiful color for a diamond is no color at all. The Gemological Institute of America (GIA) has created a scale to measure diamond color, ranging from D (colorless) to Z (yellow). Fancy color diamonds are graded Z and higher.
Most Hoppe Jewelers diamonds are graded "near colorless" - between G and I on the color scale. At a J grade and beyond, the human eye can start to detect a yellow tint.
D-color diamonds are very rare - and are priced accordingly. Moving down the color scale toward H or I lets you buy a diamond that still appears white, but is more common and thus, more affordable.
One thing to note: Color diamonds have become more valuable as they've become more fashionable, and "fancy" colors, when they occur naturally, are rare and expensive. (Diamond color treatments can help you get these coveted colors for less.)