Rej the developer has not made Caustic 3 officially skinnable but it will probably come as an official release later so if you have too much trouble or problems skinning the device please do not bother him about it... You can of course always bring up questions and suchlike on the forum and there will be help for sure.
Anyway one Caustic user hskdx started doing some beautiful skins for Caustic like the one above and Rej have left some instructions if you want to try to do some of your own.
Have not tried it myself but it does not seem to be hard to do or to download some skins
that somebody else did and change the standard ones of the different parts in Caustic.
So here is some Forum threads to read and find out how to go about it:
There is one or two more threads but these are enough I think and you can always like said ask on the forum.