colour interpolation

I’ve got to the third exercise in my new book
(a) there’s no need to rush
(b) I keep going off on tangents = the sign of a good book!
Here’s my version

Colour interpolation (finding the middle colours) is done using the RGB model above the line and HSB below. HSB uses the colourwheel so the middle colours are brighter below the line.
The mouse position controls the number of rows and columns.
Click for a new set of colours.