Kids brainstorm as many things as they can think of that are always or usually red. Use the thinking categories to help children be more flexible in their thinking. Record their responses. Tell them that when they finish naming as many things as they can think of (I list these on smartboard), they will see pictures of fifteen of the things that you, yourself thought of. The challenge is to name all of the things the teacher (you) thought of.  Kids enjoy doing this. It's a good idea to make sure you include things they probably will think of and a "few" they probably won't.  You can use this same procedure with other colors.  Kids will get better at this as you progress through colors (use thinking categories).