The Rev Dodgson said:

Alleged:

“Given the limitations of a computer screen – this is every color it is possible for a human to see…

Yes – I know it seems impossible – but each one of the smaller squares has every possible brightness of red going across horizontally – and every possible brightness of green going vertically – and each one of the squares contains a different brightness of blue. So that’s it…all of the colors there can be on a computer screen.”

But I wonder where the yellow went?

Red, blue & yellow are the three primary colours for pigment. Red, blue & green are for light.