We can build a basic color contrast system based on the current locations of mouseX and mouseY.

            @ Key Params:   mouseX -> Determine the size of  inner rectangle. 当前光标的X坐标决定小正方形的大小
                            mouseY -> Determine the filling colors of canvas background and the rectangle. 当前光标的Y坐标决定背景与四边形的填充色

            @ Interactions: Moving cursor from left to right -> Will change the size of the inner rectangle; 鼠标左右移动将改变小正方形大小
                            Moving cursor from top to bottom -> Will change the filling colors of canvas background and the rectangle. 鼠标上下移动将改变背景与四边形的填充色
        

Source code