private void panel7_Paint(object sender, PaintEventArgs e)        {            //LinearGradientBrush brush = new LinearGradientBrush(e.ClipRectangle, Color.Green, Color.Blue, LinearGradientMode.Vertical);            //e.Graphics.FillRectangle(brush, e.ClipRectangle);        }

public partial class Form1 : Form{    public Form1()    {        InitializeComponent();    }    protected override void OnPaint(PaintEventArgs e)    {        const int samples = 100;        int height = 60;        int width = this.ClientRectangle.Width / samples;        for (int i = 0; i < samples; i++)        {            Color color = FromScale((double)i / samples);            Rectangle rect = new Rectangle(width * i, 0, width, height);            using (Brush brush = new SolidBrush(color))            {                e.Graphics.FillRectangle(brush, rect);            }        }    }    static Color[] colors = { Color.Blue, Color.Cyan, Color.Yellow, Color.Red };    static Color FromScale(double value)    {        if (value < 0 || value > 1) throw new ArgumentException("value must be in [0~1]");        value *= (colors.Length - 1);        int section = Math.Min((int)Math.Floor(value), colors.Length - 2);        double t = value - section;        Color c1 = colors[section], c2 = colors[section + 1];        return Color.FromArgb(            Interpolate(t, c1.R, c2.R),            Interpolate(t, c1.G, c2.G),            Interpolate(t, c1.B, c2.B)        );    }    static int Interpolate(double t, int i, int j)    {        int value = http://www.mamicode.com/(int)(i * (1 - t) + j * t);>