This exercise really does demonstrate how colour combinations are perceived differently. It shows how colours that are close to each other in the spectrum – in this case a bright green and various shades of green/blue and blue/yellow can make an adjacent colour look slightly different but also have a flattening effect. This is most vividly demonstrated when they are viewed alongside a pairing of complementary colours (opposite each other on the colour wheel) – then the fireworks happen!
Even neutral colours such as mid grey are perceived differently in combination with different colours, see how the grey inner square looks lighter surrounded by red.
The learning from these exercise will help me to make better choices about colour in planned rather than trial and error way. For example I can see that the choice of a complementary background colour could make a painting very vibrant while a colour closer in the spectrum to others used could create a subtle effect – both choices have their place.