Next week we will be looking at painting lemons, not original but very useful when looking at how colour changes in step with value. If we just made a yellow tone (adding black) or a tint (with white) we would miss out on the richness different hues offer.
Here are a couple of images I found on the internet which illustrate how colour changes with light.
Borrowed from http://www.learning-to-see.co.uk/
I had a go reproducing the image above, trying to keep my colours and values as distinct as I could.