Enerjet by Aerotech, Arreauxbee-Hi, Part 16, Single Black Fin Mask

The body is masked off leaving the one fin that will be painted black.

Notice the tight area at the tip of the root edge. The conduit runway is almost butted up against the fin tip. I wrapped masking tape over the low end of the runway.

Again, this took three pieces of tape to follow the complex root edge shape. 

Here's the fin after the tape was pulled.