Hello, I'm a student and have no experience in painting at all. I'm posting on this forum to see if I can get some tips on how to do simple touchup. Recently I saw some scuff marks on the wall, and I decide to use the paint from the original paint can. It was such a small scuff mark (the size of a dime) that I decide to use cotton swab. I dipped the cotton swab into the paint and applied an extremely thin layer. Afterwards I let it dry. After a day, when I examined the wall from different angle, I see a difference, and it looks like a patch. I'm sure that the color is the same, but why is it that I can still spot the difference (esp. when I'm looking at it from the side) How do I fix it without repainting the entire wall? Thanks so much!