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It took a little bit of arm-twisting to persuade our moderately gray-haired test subject to try Just for Men shampoo-in hair color.

After all, this is a guy whose preferred grooming product is water. (Just wet it and slick it down with a brush.)

But with the promise of help from a household member much more familiar with the hair-coloring process, he gamely offered up his salt-and-pepper ‘do.

The kit ($6.50; available at Walgreens, Osco, Target and similar stores) comes with the hair color, applicator bottle, man-sized plastic gloves and step-by-step instructions. Timing is an issue, and the instructions exhort users to “Apply quickly! Take no more than 3 minutes!” A watch with a second hand gave our test subject–an engineer by profession–a modicum of comfort: something to measure precisely!

After the 3-minute application, the hair color takes 5 minutes to work its magic; our skittish test subject hit the shower and shampoo after only 4 minutes.

(Cautious users will want to take the allergy-patch test before coloring their hair. Unpleasant reactions to the dye are a possibility.)

The good news: The color turned out great, taking about 10 years off his appearance. He got the hoped-for darker look on top, with touches of gray remaining in the sideburns.

Reaction from friends and co-workers was a non-event. Only his boss noticed and commented, favorably. His 20-year-old son, seeing Dad after being away from home all summer, was oblivious to the change.

That brings us to the bad news: It’s probably too subtle for anyone heading into the Witness Protection Program.