1. Enchroma Color Test: http://enchroma.com/test/instructions/
This is a great test to check yourself for color blindness.
2. Colorful Shepard's Tone: http://www.fallingfalling.com/
Let's you hear the Shepard's Tone Illusion while looking at colors falling.
3. Pantone Smoothies!: http://pantonesmoothies.com/
Precisely color code your food, It'll tell you how much of an ingredient you have to add so you can have the perfect color smoothie.
4. NSkyC - Color of the sky in New York: http://nskyc.com/
Calculates the average color of NYC's sky every 15 minutes.
5. Online Color Challenge: http://www.xrite.com/online-color-test-challenge
Arrange the colors from one hue trough to the other.
6. Factory Balls: http://www.bartbonte.com/factoryballs4/
Reproduce the color pattern and shape of the ball being shipped.
7. Animagraffs by Jacob O'Neal: http://animagraffs.com/
Detailed animations to explain how simple objects work, you can even learn how to moonwalk!
8. This Is Sand: http://thisissand.com/
Already Covered in: "How Secure is Your Password? And 21 Other DONGs"
9. Adobe Color Wheel: https://color.adobe.com/create/color-wheel/
Already Covered in: "The Most Exclusive Website in the World? -- DONG"
10. Color Clock - The Moment of Color: http://bickov.com/projects/the-moment-of-color/
Every second you get a different color.
11. Carnovsky - RGB: http://www.carnovsky.com/RGB_BLACK_wallpapers.htm
In natural light, they look like normal paintings/pictures but under different lighting they change.
12. Electric Boogie Woogie: http://www.electricboogiewoogie.com/
Animated version of Piet Mondrian's Broadway Boogie Woogie.