Todays demo. i started painting everything as five different values of purple and then blotted it off so it wouldnt mix with what i put over it. see the purple remnant up in the far right top corner. you can faintly see other purple spots in the light green part of the table top. the purple and green are so close in value that i can leave parts of the purple unpainted and it doesnt shout "paint over me, PLEASE!" Thats how you know you have the values similar when you can hardly tell the difference between whats down and what you put over top of it.
then i mixed the real color and applied making sure that it matched the purple value i assigned each shape.
lastly, i showed the class how to put in the highlite on the pepper, blur the appropriate edges, and put a few finishing touches on it.
this is what i ended up with. done in less than 45 minutes.