We are often asked if the countertop of the island needs to match the existing kitchen countertop in style, or what will be installed as the main kitchen countertop. In most homes I would say it does match, but it really does not have to at all, nor does the material need to be the same. In fact, if you are not going to match them up exactly it's better if it looks like you are not even trying to match them, so using a completely different color and surface is perfectly acceptable.
Regarding colors and designs, kitchen islands can be made from a number of different materials. The framework is usually wood, but the main visible surfaces could be metal or even stone - granite is a popular substance used for counter tops. Stainless steel is also good, but try to avoid aluminum if possible, because that is very soft and easily cut and scratched, and the metal oxidizes to a dull finish.
Plan the height of your cabinet appropriately. Since most islands will have at least two stools or chairs pulled up to the surface, you may want to think about the seating or stools first. There are two kinds of bar stools with one being much higher than the other. Unless the island will be used primarily for family eating, there really are no hard and fast rules on height. It does not have to match the height of the kitchen cabinet, but often does. If it is not going to match it should be taller in most cases.
For example, we have seen islands of concrete when the rest of the kitchen countertop is made of granite or another material. We have seen a black island used as a nice "dividing wall" to keep the kids away from a white kitchen.
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