FRCP is an acronym for Fiberglass Reinforced Co-Polymer. Similar to FRN, glass fibers are mixed with a co-polymer (instead of nylon). The handles of the knives that feature FRCP as material are made by injection molding which allows to produce large quantities easily.
Spyderco uses FRCP on its cheaper models (at the time of this writing, only on the Manix 2 lightweight) but that doesn't mean that the material is inferior. In fact it is a very durable and long lasting material for knife handles. Besides being available in opaque colors, FRCP can also be transparent (and colored transparent variations).