Is it possible to only use one color of an RGB LED strip?
Doxylover is right.  most inexpensive RGB LED strips have four conductors; the three colors and ground.   The ones I've used can take variable voltage on each circuit to allow color mixing and dimming.  

Are you looking to have variety in color?  or just a stripe of a color to accent?  

I think your boat is going to look fantastic.   Nice lighting.