Here is an easy activity to do even if you don't have fancy colour sorting equipment. Place a piece of construction paper, in the colour you wish to teach, on the floor. Name the colour of the paper first. Begin looking around the room for toys of that colour and place them on the paper. State what you are doing to the kids, and ask for their help. It is best to choose objects that are uniformly that colour, to make it clear.
We did the activity this week, using the colours red, yellow, and blue. As a teacher, it is instinct to reflect upon activities or lessons. One thing I would do differently next time is to use larger pieces of construction paper to put the objects on (or tape smaller pieces of construction paper together). Also, if children choose a toy that is not uniformly that colour, but communicate to you where they see the target colour, obviously encourage them, and let them place it on the sheet. Lastly, the activity was very brief. Kids' attention spans wander in the blink of an eye. I don't believe that it makes this activity unsuccessful though. It just means that I can work it into the program a few times a week to make it more effective, especially with such an easy set-up. I am already thinking of other ways to revise this activity, so stay tuned!