Why is my screen displaying RGB? and how to fix

I was changing my cars scale when all of a sudden I must of clicked something and now all my unreal engine stuff looks red / green / blue. https://puu.sh/yRxvv/ccdedda844.jpg any idea what I clicked and how to fix it?

This is how all my projects looks now, now just this one.

You switched to Lightmap Dencity display mode, click the “Lightmap Dencity” that you see in corner of viewport (2nd button) and you can find many modes which can be useful for you like Shader Complexity which allows you to see which materials are expensive in scene or Unlit if you want to see textures in dark places, you can also switch between different buffers that are used in scene composition like normal maps or roughness etc… The standard mode is called “Lit”. you can also switch modes by pressing F buttons in play mode.