A warm-up problem is illustrated below: Suppose that like repels like at a distance of two, and the only strand types are aqua, blue, crimson and dark yellow.

• 下图是一道暖身题：我们将条件改成，假设在三个相邻的圆环内，其颜色是互斥的，而且只使用浅绿、蓝、深红、土黄四种颜色。