Color Illusions are images where surrounding colors trick the human eye into incorrect interpretation of color.
You may want to hide some parts of the illusions by your hand so that you don't get distracted by the rest. You may even use some online color picker tools to verify that the colors are identical.
Don't let your eyes trick you :-)
Dress Color Illusion
Is this dress "white and gold" or "blue and black"? Millions of people voted at buzzfeed.com and around 70% see the dress as white and gold. So are the remaining 30% wrong?
Nope. Actually, what you might see as white is actually blue. Cover everything else and look at just a small part without any surrounding colors. You'll see it's blue. (posted originally by swiked on tumblr)
Same Color Illusion
Also known as Adelson's checker shadow illusion (published by Edward H. Adelson) depicts something hard to believe. Square marked B looks considerably lighter than square A, due to the "shadow" being cast upon it. However, color on both squares is precisely the same shade of grey. If you don't believe, use any eyedropper tool or print/cut the squares to verify that both square A and square B are precisely the same.
Believe it or not, but the pieces A/B/C all have the same color. Use any color picker, graphic program or simply cover the remainder with your hand to see for yourself.
The upper chess set is black and the bottom set is black, right? Wrong. Both sets have absolutely the same color, just the background changed. (by Barton L. Anderson and Jonathan Winawer)
Red vs Green
When you first look at this, how many colors do you see? Some might say they see 3 or even 4 colors, but there are 2 - red and green! People usually think they see 2 shades of red, but there is only 1. Look closely and you will notice on one side that white boxes surround the red boxes, and on the other side, green boxes do! Due to the placement of these boxes you get the "illusion" of different colors. Since white is not considered to be a color (it is the presence of all colors in scientific terms) we can safely say that there are 2 colors present here! Still don't understand?
Also known as Pac-Man illusion is another example of afterimage complementary color (green as opposite to lilac). Follow the movement of the rotating pink dot with your eyes and the dots will remain only one color, pink. But if you stare at the black + in the center, the moving dot will turn green. (by Jeremy L. Hinton)