Bevil Conway, a visual artist and neuroscientist with the National Eye Institute broke it like this to Motherboard: "You brain says, 'the light source that I'm viewing these strawberries under has some blue component to it, so I'm going to subtract that automatically from every pixel.' And when you take grey pixels and subtract out this blue bias, you end up with red."
We're used to stuff looking a certain way, and our brains course-correct for us. So next time you're sitting in the shade, and the light catches a strawberry as you're about to pop it in your mouth, know that color constancy helps you perceive its true colors instead of making you believe it's started rotting. Good thing too, because strawberries taste great.