Acrylic paints are water-based tubes of paint, that cost anywhere from $2 to $7 apiece. You can buy them at any craft store; in our area, Michael’s has them. Or you can go to an art supply store, where they’re more expensive.
But even at $7 a tube, they’re well worth it.

An old pro introduced me to the paints years ago. We have top-nailed floors in this area, and he used acrylics to paint out nailheads on areas where he couldn’t risk setting the nails because of old flooring. I’ve used acrylics to paint in grain, hide scratches, and match existing stain color on one new board. I’ve painted out silver edger scuffs on stone or marble fireplaces, and also painted in edger knicks on bricks.

I have three basic colors for floors: yellow, tan, and dark brown. I put a portion of each of them on a piece of cardboard, and dab in them with the brush until I get the exact mix I want.

On floor surfaces, they dry quickly—within minutes, I can coat them.
If I don’t like the color, I have to wipe it off immediately—these set up fast.

We also use brown and black Sharpie pens to draw in grain, and we soften it up with the paints. Sometimes we’ll create a fake joint, with a utility blade and a Sharpie, and this helps us hide a scratch that is in the middle of a board.
We can color in the scratch and make it look like end grain at the fake joint.

Mohawk sells a floor repair kit for $350, that’s designed to do this kind of touch-up. I’m able to do a lot of the same processes for about $25 worth of paint tubes and brushes.

Tinting new boards to match existing finish is the most useful thing I’ve found. It is hard to get an exact match with stains alone; especially if you need red or orange shading. I stain the new board with a stain that’s close to the right color, and put on at least one coat of poly. Then I fine-tune it with the acrylics.

With the paints, you do the color mixing right there, and you can see when you’ve got the color locked in. I wet the brush, smear it in the paint, and create a kind of glaze that I rub on with a rag. It goes on like a film, and it dries immediately. Sometimes it takes more than one application—I keep adding layers until I get the color I want. The end result is good—the customers have been very happy with the patches. This is especially useful for those old tan-colored floors that don’t match either new ‘pink’ red or new ‘gray’ white. I’ve been able to match new boards on floors that had clear finishes.

I had some pictures of this process, that were lost in the transfer to my new phone. If I get more pictures, I’ll post them here.

Thanks Farrell:

I've been trying to get a signature up there for you. If you look in your own control panel you should see it. Unfortunately it doesn't appear "live"

You know by now this phpbb stuff is not my bag at all. Maybe there's an activation on your end?

I've been tempted to get the kit or one over at cal-flor.com. Keep getting calls for plank repairs and sometimes a little touch-up works just fine. I think I'll give it a shot, thanks.

It's a great skill to develop. I work with a decorative painter that can do all theses things . Most of the time, you can go to your favorite paint store and buy their universal colorants. These dissolve in oil or water . I use yellow oxide and red oxide .And sometimes I use a little basic brown. Or a pinch of black to tone the color .

Also, you can mix colorants into water or oil based glaze to create transparent colors if you don't want to use a finish as the carrier.