uLearn.Photography - part of FilmPhotoAcademy.com
Make a collection of different coloured objects, say yellow, red and green peppers.  The more colours you can find the better.
Take (or make) a black and white photograph.  
How dp the colours show as tones of grey?   
Can you always see the difference between the different colours or do they look the same?
Go through photographs you have already taken, if you convert them to black and white do they look better, worse or the same to you?
Which types of photograph look better?
Which types of photograph look worse?