Juiciness and Sassyfras (23 months) are learning their colors. We do many activities around our "color of the week". This week is blue. We'll color, paint, and make play dough in blue. We'll eat blue foods, wear blues clothes, and find blue objects.
I've devoted a kitchen drawer to our efforts. It contains all blue toys and only blue toys. It's so much fun to start the week with them running to the drawer and hollering, "Yellow", but by the end of the week they'll be hollering, "blue". Only to start the following week hollering, "Blue" to an all red drawer. It will take them some time to learn each color, but we'll have fun in the meantime.