I bought adhesive mylar strips from Campmor and stuck two on each face
of both blades. The mylar is so thin that there is no worry about
disrupting the flow over the blades.

I have received unsolicited, positive feedback from other folks. Most
of the comments sound like: "Damn, I coud see your paddle flashing from
way out!"

Of course it is most effective when paddling east or west but it does
seem to work well, and the strips were pretty cheap.