Are your piano keys stained, yellowed, cracked or chipped?  White key tops and sharps can be replaced with new plastic molded tops and fronts.   The process is a simple one of routing off the old key tops to the depth of the new replacements, which are usually slightly thicker.   The new tops are then glued on with appropriate adhesives.   The process is illustrated below.

In the photo to the left, the center key is how the originals looked before replacement. The two outer keys have new key tops.