The cut of the diamond allows natural light to enter into the heart of the stone and reflect back, which gives the diamond its original brilliance and fire. To put it otherwise, the sparkle of the stone depends more upon the cut quality of the diamond than on its color grade. Yet again, a D stone will emit maximum luster and radiance when compared to an H stone.
The GIA diamonds in the color range D to Z, but there are naturally colored diamonds too, which do not fall under this grading. Take, for instance, a blue diamond; its natural blue hues will surely affect how amazing the centerpiece looks in an engagement ring, but even more, if it were cut in a perfect heart shape.
Although some would say that cut quality matters a lot more than color to get the best light performance from a diamond, it actually depends upon the preferences of the customer to evaluate cut and color when it comes to buying a diamond ring.