It depends on a few factors. Like, how much natural light hits the wall in the areas of the touch ups, how long ago the room was painted, which sheen and brand of paint was used, etc. Some brands touch up better than others. You want to simulate the texture that is on the wall already to give your touch ups the best chance to blend in. If you can use the same nap size roller cover that was used when you painted the room that would be best. Darker colors are harder to get to blend in than light colors, so with yellow you may have a shot.

Thanks for your reply paintguy! My house gets lots of natural light. Is that a bad thing for the touch up? The house is only about 1 1/2 yrs old, the builder's model. They used Benjamin Moore Golden Straw in eggshell I believe. Builder lives down the street so maybe I can find out about the nap size. I guess if worse comes to worse it won't kill me to repaint the whole wall. Thanks again.

I don't believe the color will match.

If you know the color there is a very good chance you can biy more and get it to match. I have done this several times and you can not tell where I touched it up. They were all fairly light colors. I even touched up a bedroom that had been painted about 12 years before(luckily I had the code) and it matched perfectly. If it doesn't match, then you might need to repaint completely.

"If it doesn't match, then you might need to repaint completely."

You can almost always get away with one wall.
Light rarely hits multiple walls the same way in a room, so as long as the color matches from corner to corner it looks fine.