Estes Little Joe 1, #7255, Build Part 14, Hit & A Miss!

One fin is painted orange. On the left is the mask.

I set a triangular piece of Scotch tape over the very outside edge of the fin to leave it silver. That's a Sharpie blackened triangular piece of Scotch tape. The original Little Joe I had silver on the outside edge. This mask turned out very well. On a mask like this, smooth root edge glue fillets are needed.

Rather than do a difficult mask, I thought I'd try some spray paint decals.
TIP: I sprayed some orange paint on one half of a print at home white decal sheet. Pieces are cut with a new, sharp knife blade, a dull blade can crack and chip the paint. Soak and transfer like any other water slide decal. You can do this for some trim, it has worked well for me in some applications.
I normally don't use Krylon, but found this on sale. It sprayed on very smooth and dried quickly.

No clear coat is needed - the paint seals the surface.

A tracing of the fin was made. That rectangle on the right side is the orange trim on the outside of three fins.

The rectangle was drawn on the other side of the leading edge crease.

The spray paint decal was cut to make these "Vs". The tracing template makes a one piece decal that will conform to the leading edge and roll straight down the sides of the outside edge.
On the right is the placed decal before trimming the overhang.

While it looked okay, I was concerned about the strength of the decal at the fin tips. With the model standing on a table the corners could crack and chip off. I wasn't able to use these decals and they were removed.