I was left with the thought - what is the simplest book I could write that explains "What is Red?"
What is Red? (first attempt - you'll have to imagine the pictures)
Sunlight looks white.
Water can split up sunlight.
When sunlight is split up you see a rainbow.
Sunlight is made up of all the colours of the rainbow.
Red is one of the colours of the rainbow.
This white light is made up of all the colours of the rainbow too.
A glass prism can split up white light.
When white light is split up you see a rainbow.
This is a blue light.
A glass prism can't split up blue light.
The blue light is made up of only blue.
This tomato is red.
It looks red when it is in red light.
It reflects the red light.
This is the tomato in blue light.
The tomato looks black.
There is no red part of the blue light for it to reflect.
The tomato looks red in sunlight.
It reflects the red part of the sunlight.
Red is what we see when the red part of sunlight shines on things that reflect red.