I squinted my eyes and covered the screen watching this video by Tom Scott because I don't want to have coloured vertical and horizontal lines ingrained in my vision. So I suggest you do the same and look away. No, seriously. Don't look too long or you're going to start seeing stuff that's not actually there.
It's called the McCollough effect which basically means black and white gratings can appeared coloured after you stare at red and green gratings. It's an aftereffect, so your vision of things will change after a period of induction. As explained here:
For example, if someone alternately looks at a red horizontal grating and a green vertical grating for a few minutes, a black-and-white horizontal grating will then look greenish and a black-and-white vertical grating will then look pinkish. The effect is remarkable for often lasting an hour or more, and in some cases after prolonged exposure to the grids, the effect can last up to three months.
Don't say we didn't warn you. Do not look at the images in this video for too long.