When my oldest two kids were under three we often had "theme days." I felt like choosing a theme like specific colors made the planning easy.
I remember a blue day when we had blueberries with our breakfast and blue milk, blue hard boiled eggs (from Easter egg coloring kits- but you could just use food dye and follow the directions on the box), colored with different shades of blue crayons, pointed out blue objects around the house, and even dyed the bubble bath blue with food coloring.
I think it was after several days of different colors that we had an activity one day with colored water teaching our primary colors and secondary colors by mixing them.
If you're feeling adventurous you can even make your own playdough in your theme color. I like to use this recipe posted about here. I don't usually add the glitter though. I personally don't like the smell of store-bought playdough. So if we're not making peanut butter playdough than this is what we use.