I don't remember when I told people I was going to write a tutorial about quick and dirty color correction but I said that and it's unfortunately what I'm good at so here we fucking are. Just FYI, all the screenshots of a program are Photoshop CS6 but there's some GIMP explanation too where I can provide it. Some stuff doesn't translate to GIMP, though, but this basic information will work in any program you might have that has a color balancing tool.

( We're using Goosebumps (2015) screencaps because that's what I'm iconing right now. )