When you look at a picture of a lemon on a digital screen - a phone, tablet, or desktop- what colour is it? If you answered yellow, you're wrong. To find out why, watch this neat video by Vsauce called "This is not yellow". It explains how digital screens can fool our brains into seeing certain colours, even when those colours aren't actually being displayed. And as a bonus, the last half of the video shows some optical illusions by modern artists and even electricity given off by fruits.