DEMONSTRATION:

Half-hour painting from memory

With the photograph turned over, start as quickly as you can and resist the temptation to cheat by looking to check anything: just do your best with what you remember.

Work purely from memory, using the pre-mixed colours on your palette. It is hard to try to remember the colours and values as well as the shapes and how they fit together, which is why I suggest mixing pools of the main colours before turning away from the photograph.