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We made our own optical illusions.

Here's an illusion we found.

How many shades of blue can you see?

Most people will say they see dark blue lines and light blue lines.

Actually there is just one shade of blue in the image.

The blue lines in the first, third and fifth rows are mostly surrounded by black, so they appear dark.

The blue lines in the second, fourth and sixth rows are mostly surrounded by white, so they appear lighter.

The surrounding colour influences how we perceive the blue.

Still don't believe it? You can see the exact same image without the black lines here. All the blue lines are the same!