Read the "COLOR OF THE INK" in the words out loud.
When the name and the ink color are different, most people slow down. When you try to say the ink color, you cannot avoid reading the word. If the two bits of information conflict, your brain struggles to work out what the correct answer is, and it takes longer. This is called 'The Stroop effect' and was discovered in 1935 by John Ridley Stroop.
Is the rectangle in the center all the same shade of gray from left to right?
YES, it is all the same shade of gray. An illusion of color or contrast difference can be created when the luminosity or color of the area surrounding an unfamiliar object is changed. The contrast of the object will appear darker against a black field which reflects less light compared to a white field even though the object itself did not change in color. Similarly, the eye will compensate for color contrast depending on the color cast of the surrounding area.
What do you see?
Most people see a triangle in front of three circles. Your brain tries to make sense of this pattern by going for the most likely explanation. In this case it is a white triangle in front of 3 colored circles. Even when you know that the white triangle does not really exist, your brain still opts for it as the most likely explanation.
Count the "black" dots.
It's impossible - as soon as you focus on the black dots, they disappear! Your eye and brain have very special mechanisms for seeing edges clearly. This allows you to see a sharp boundary between an object (e.g. a person or a building) and the background.