//设置按钮透明
            this.BackColor = Color.Transparent;
            this.FlatStyle = FlatStyle.Flat;
            this.FlatAppearance.BorderSize = 0;
            this.FlatAppearance.BorderColor = Color.White;
            this.FlatAppearance.MouseDownBackColor = Color.Transparent;
            this.FlatAppearance.MouseOverBackColor = Color.Transparent;
            this.FlatAppearance.CheckedBackColor = Color.Transparent;

最近我也在鼓捣这个,自己对照看看
你赋的值是0,0,0当然是黑色了

E_button.BackColor = System.Drawing.Color.Transparent
E_button.FlatAppearance.BorderColor = System.Drawing.Color.Transparent
E_button.ForeColor = System.Drawing.Color.Transparent
不知正确否。