Halloween costumes are out in all the shops so I figure it's ok to mention it now.
I saw these scary pumpkins a few years ago and thought they were really eyecatching.
I gave my kids some red and yellow paint and they mixed them on their page to make the Orange they wanted. They painted a pumpkin shape and we let them dry.
The next part of the lesson takes a bit longer. They kids cut out their pumpkin and glued it onto a black page (A3). They then cut out a mouth, teeth, eyes, and grass from coloured paper.
I try not to give a huge amount of instruction as I prefer the kids to be creative. However before they paint their pumpkin I ask them to make sure their pumpkin is big and fills the page! Nothing worse then having a tiny pumpkin!!!
If you try this out let me know how your class get on. :)