Yes, you can tint cinnamon buttercream with food colouring in the same manner as any other buttercream frosting. Due to the shade of the base buttercream, which will be light brown from the ground cinnamon, there will be some impact on the types of shades you can achieve. If you are wanting to make a deep colour, such as a burgundy, purple, blue or brown you may find these easier to achieve since the cinnamon will help to deepen the colours. Lighter shades or pastels may not turn out as well. You will not be able to make this frosting white.