I really like the Rainbow reaction between sodium hydroxide, sucrose, an potassium permangante :)
You could make your own pH paper:http://www.sciencebuddies.org/science-fair-projects/project_ideas/Chem_p041.shtml This one is colorful. It's relevant to the subject of chemistry. Looks kinda easy too.
Tri Nitro Tolulene! No, they wouldn't like that. How about penicillin? Lots of sites will say it's really complicated, but it isn't. You'll have a tougher time growing the bacteria you want to kill than you will the penicillin.
http://tinyurl.com/yfl5ljx Apart from that, I would suggest something explosive. Or you could make vodka, that's chemistry, or at least the distilling is. You could also cook a steak and explain the chemical changes going on. I luckily haven't had to do any projects at school all year (my school year is also over). Thinking of it, I've only had to do 2 projects in the entire year.
dry ice bomb
A demonstration of how volcanos work, using Diet Coke and Mentos.You didn't say it had to be a good idea.