"The Sky is Blue"
Actually, the sky is no color at all. Any color is an illusion but if you want to believe it is blue..
If you were in Seattle right now, you would agree that the sky is not blue. Look up, observe, and you will see that it is grey, just before that little drop of water hits you in the eye.
What the hell are you talking about? Color is not an illusion, it's a sensory perception based on the wavelengths of a short band of 'visual' electromagnetic radiation.
As for the sky not having color, that's silly as hell. Here is an experiment. Take a digital camera outside, take a photo of the sky. Isolate the sky and do a palette check on the coloration, I assure you that the blue represented by the numbers are not illusory. some of you are such screwballs, That's a tired old "trick" question, the sky is perceived as blue and IS blue. I understand the "logic" behind the trick, but it's really a retarded assumption. Sky is an abstract noun, as it really has no substance, and is a location rather than actual object. Places cannot have colors of course, as is the inception of this annoying trick question. However we give substance to the sky as an abstract object and thus it can have a color. Taking a photograph of the sky shows many variations of the coloration. The argument is not whether it has color or not, but rather on the ability for a location to have coloration. The abstraction of this allows for it to. End of story.