My Screen Looks Like a Negative

Hello, I am hoping that someone out there can help me. Everything on my computer is colored like a negative. As in a negative from a photograph. When I say everything, I mean the desktop, the internet pages, mac word etc.. The white backgrounds are black, the letters are white. When i pick a font color, yellow looks blue, pink looks green. I do not know what happened. I left the computer on the desk and on for a couple hours. Possibly one of my kids did something. I have searched high and low on this computer. There must be an "effect" button, as there is on a camcorder. I restarted my computer as well. Can anyone help me? Thank You in advance!