Occasionally, I get comments from clients telling me that I’ve used the wrong color on their website–that there are two different blues or oranges on the same page. When verified, however, I’m almost always able to tell them that the colors are generated from the same hexadecimal color value; they are exactly the same. Most often the optical variation occurs because of the neighboring colors. A combination of colors can change the way that we perceive an individual color. This illustration is a wonderful, but hard to believe, optical illusion demonstrating this principle.
The blue swirl and the green swirl in this image are the same color. See the article