This GIF might break your brain a little:
Take a look at the sequence of images below (I recommend clicking through to enlarge, Tumblr Dashboard folks). Works best if you stare at the dot:
Color? Or black and white?
The rods and cones of your retina respond to the illumination (black-white) and color of a scene, respectively. But that input passes through one key information filter on the way to your visual cortex.
In a sense, your rods and cones take a wavelength survey of the visual field, measuring all the wavelengths they are capable of measuring. It’s the “opponent process” that begins to give color meaning. It’s not only how “red” something is, it’s also how “not green” it is. Likewise, a yellow tulip in the original image from above is intensely “not blue”.
When looking at the “blue” tulips, your blue photoreceptors get fatigued. This creates the illusion of yellow when the blue surplus is taken away.
Ouch. I need to close my eyes.