//(梯度刷)
                  LinearGradientBrush lbrush1 = new LinearGradientBrush(rect1,
                  Color.DarkOrange, Color.Aquamarine,
                  LinearGradientMode.BackwardDiagonal);

//(阴影刷)
                 HatchBrush hbrush1 = new HatchBrush(HatchStyle.DiagonalCross,
                  Color.DarkOrange, Color.Aquamarine);
                  HatchBrush hbrush2 = new HatchBrush(HatchStyle.DarkVertical,
                  Color.DarkOrange, Color.Aquamarine);
                  HatchBrush hbrush3 = new HatchBrush(HatchStyle.LargeConfetti,
                  Color.DarkOrange, Color.Aquamarine);

//(纹理刷)
                  textureBrush = new TextureBrush(new Bitmap(@"e:\123.jpg"));
                  //e.Graphics.FillRectangle(hbrush1, rect1);
                  //e.Graphics.FillRectangle(sbrush1, rect1);
                  //e.Graphics.FillRectangle(textureBrush, rect1);
                  e.Graphics.FillRectangle(lbrush1, rect1);

------------------------------------

using System.Windows.Media;

1、String转换成Color

Color color = (Color)ColorConverter.ConvertFromString(string);

2、String转换成Brush

BrushConverter brushConverter = new BrushConverter();
            Brush brush = (Brush)brushConverter.ConvertFromString(string);

3、Color转换成Brush

Brush brush = new SolidColorBrush(color));

自己的：

获取颜色对话框中选择的颜色

  if (e.Button == System.Windows.Forms.MouseButtons.Left)

            {

                Color col = new Color();

                if (this.colorDialog1.ShowDialog() == DialogResult.OK)

                    col= colorDialog1.Color;

                SolidBrush colorBrush = new SolidBrush(col );

                //获取鼠标点下的位置

                Point p = new Point(e.X, e.Y);

                //判断鼠标点下的位置是否包含在矩形里面，以此判断是否选中某个矩形

                if (rect.Contains(p))

                {

                    Graphics g = pictureBox1.CreateGraphics();

                    g.FillRectangle(colorBrush , rect);//填充颜色

                    g.Dispose();

                }

            }

4、Brush转换成Color有两种方法：

（1）先将Brush转成string，再转成Color。

Color color= (Color)ColorConverter.ConvertFromString(brush.ToString());

（2）将Brush转成SolidColorBrush，再取Color。

Color color= ((SolidColorBrush)CadColor.Background).Color;