The resin inside fin boxes is black. I bought a new carve 121 and within days the resin in the fin box well just under the screws had shattered. This is not uncommon, but in this case the the resin fractured more each time the board was used. I informed the dealer and got permission to replace the resin. It was easy to remove the resin using a wood chisel and a mallet leaving the glass fibre of the box intact. I had black pigment for polyester resin but I ended up opting for the powder that is used to dye concrete. I mixed the black concrete dye with epoxy, plugged the screw holes with a plastic rod and poured resin into the well. It was then necessary to get the well level and measure that the depth was right using a callipers. When the resin began to set I removed the plugs put cling film on top of the fin root and wiped it with wd40. I then drove my best fitting fin into the box using a mallet. This pushed some resin through the screw holes and gave a final shaping to the resin in the well. The rein retained its black colour over the following three years that I had the board and was indistinguishable from the colour on the sides of the box.
When I sold the board I explained what had been done.
I regarded this course as an easier option than making a claim under the warranty, especially having been told by the dealer that this cracking is common and harmless.
The repair never cracked in three years of use and the colour did not change.
This is a statement of experience rather than a recommendation of procedure.