1Two things to know first
Your eyes have color sensors — and they get tired
You need two small ideas. Watch each one happen:
Three kinds of sensors
The back of your eye has tiny sensors in three flavors — one likes red, one likes green, one likes blue. Mixed together, they tell you every color.
Stare = they tire out
Keep one flavor of sensor staring at the same color and it gets tired and fires less — like an arm that gets shaky after holding still too long.
2Fresh sensors vs tired ones
When the answer is balanced — and when it isn't
All fresh → plain white
Look at a white wall and all three sensors fire about the same. Balanced sensors say: white.
Red tired → off-balance
Tire out the red sensor, then look at white. Red can barely fire, so green + blue win the vote. Keep this in mind…
3Tire out a sensor yourself
Drag to wear down the red sensor
Here are the three sensors looking at a white wall. Drag the slider to tire out the red one and watch what color the eye ends up "seeing" when red drops out.
As red gets tired, the leftover green + blue tip the eye's answer toward cyan — the opposite of red.
4Now predict a new color
What happens after green? 👻
You explored red. Now apply the sensor rule to green. This on-screen model draws the afterimage so everyone can follow; it does not measure what your eyes see.
Guess before the model runs
After green sensors adapt, which heart will this model show on a white background?