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I’ve been paying a lot of attention lately to colors on flies and using fluorescent “hot spots”; focusing more on how fish see flies underwater than how they look in my hands above the surface. We know, for example that certain colors dissipate in deeper water due to the decrease in light penetration. The deeper you go, the grayer it gets.

While we can debate whether fly colors really matter much compared to other factors like size, profile, and so forth, I don’t think it hurts to add a little eye-grabbing detail, particularly when you’re fishing attractor patterns, and especially when you’re fishing nymphs in deeper runs when the water is off-color. As a rule of thumb, I think it’s best to mimic natural bugs as closely as possible when you know fish are keyed on a specific food source. But when you’re prospecting, any and all “attention getters” are worth a shot.

This new Spectrum Response U/V spray is distributed by Westwater Products, and it’s designed to make colors pop on your flies. Squirt it on a surface like fur or feathers and it causes those materials to absorb radiation in the ultraviolet region of the electromagnetic spectrum, and re-emit light in the ultraviolet regions of the spectrum. In simplest terms, it makes flies appear brighter when the water is darker. The theory is pretty simple: Fish sees fly better; fish is more apt to eat said fly.

The 2-ounce spray bottle costs $19.95, and I’m told a 1-ounce bottle will soon be available for $12.95. The spray is non-toxic and hydrophobic, meaning it doesn’t wash off of treated surfaces (so you want to be careful not to spray your tippet if you don’t want that to shine also). It doesn’t involve resins that will gum up your flies. One tube of spray goes a long way; it only takes a squirt or two to treat a fly.

If you’re looking for an advantage but you’re not willing to go so far as to scent your flies (that would be a low-down dirty trick, after all), this might be $20 well spent. Then again, it might not be what you’re after. But experimenting with different flies (sprayed or not), different materials (fluorescent fibers or not), and different water conditions would be a lot of fun, and I suspect the results would change the way a lot of anglers think about colors on their bugs (and lures, for that matter).