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.

I have been successfully touching up paint for years by brushing the color on the spot, then going over it with a *dry* roller. The roller completely gets rid of any brush marks and blends the new paint in. If your ceiling paint is flat, then your touch-up will be practically invisible. If you buy a new quart of the same color, there may be some shade variance, but unless your ceiling is really dirty you probably won't notice it after the first week or so.

It was hard to take pictures of the texture because it is very subtle. Even from a few feet away, it looks like the wall is only very slightly textured drywall. I was able to take these with very bright, direct light. I increased the contrast to make the texture easier to see but I'll post the original picture, too. I think they used a roller and then blended out the edges with a brush?? I was able to blend the touch ups that are near the light brush strokes with a small paintbrush. But my other touchups stand out because they are too smooth. I think I need to use a different type of roller? I also noticed this when I was taking the pictures. It's a windowsill, and it's the only place I've found that looks like this, and I don't know if it's the paint or drywall. With the exception of art painting, where I am conscious of my brushstrokes in a different way, I've never painted anything in my house with the intention of leaving a texture before - it's like the opposite of everything I've practiced. I have painted a lot of furniture and cabinetry, and I practiced so much to learn to lay thick adhesion primers without strokes! And back then I couldn't find any tutorials about proper technique, I just sort of experimented until I figured out how to do it. So, I'm not exactly sure how to manipulate it, and if there's a proper technique I should learn.

I'm not sure anything that becomes rigid when dry is going to be a good choice because the way the wood of the wall and floor will expand and contract differently with changes in humidity. I think a color matched caulk would be a better choice. In addition to the "general construction" type caulks you might also want to look at caulks that come the companies that make tile grout. Many of companies offer dozens of colors, maybe you can get lucky there. Frankly you'd be better off using some kind of little wood moulding. There's a reason they invented the stuff...