The month of Colours always includes a major Wall Activity called "Clouds of Colour Kingdom". It has a touching original story set in the Middle Ages, simplified to entertain toddlers and preschoolers.
Another part of your Tots' day during the month of Colours, is glueing the Colour of the Day into little booklets. Youngsters love learning how to glue and paste! So even if a child knows all his colours, the colour-related activities will keep him well amused.
Each day's worksheet features a large "shaped" outline portraying the Colour of the Day. The Fundamental of Colour is the simplest of the four Fundamentals; it's always fun to introduce the worksheets and the other activities in the daily schedule.
From my experience, if I have a four-year-old who knows her colours, and a two-year-old who has no clue about colours: while doing an activity, the four-year-old can name that colour immediately while the two-year-old gains an understanding of that colour from the older Tot. It's not boring for the four-year-old, and it's not too challenging for the two-year-old.
Although colouring a shape is a simple activity, not requiring many art skills, it still helps children practise with colours.