If you are sensitive to flashing images please do not read further.

There is a flashing image lower on this web page and you should only look at it if flashing images make you feel somewhere between neutral and great.

The image is made of a red square and a green one, with the red and the green switching spots ten times a second. In the centre of each square is an x.

If you are sure you want to do this:

Stare at the two x’s. Let your vision go a little blurry, until the two x’s overlap into a single one, as if you are trying to see the dolphin in the autostereogram on the wall in the dentist's office.

You may have an easier time getting the x’s to merge if you use your phone and hold it up close to your face.

Pay attention while the red and green flicker, and observe that the colour you are seeing in your mind behind the merged x is neither red nor green but really is both reddish and greenish at the same time.

There is no wavelength of light for this colour, and no combination of pigments will paint it. Brain red green is only for in your brain.

Stare at the brain red green until you have words to describe it.

After a long time please write the words down and post them on the internet.

If you are still doing OK despite the flashing images, you might enjoy this quicker version of the same picture, which flickers at roughly 24 frames a second.

If you are not doing OK, I apologize.