Color Shades and Tints

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Windows.Forms;

namespace ColorShadesAndTints
{
    public partial class Form1 : Form
    {
        List<Color> colorList = new List<Color>();
        Color myColor;
        public Form1()
        {
            InitializeComponent();

        }

        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            int l = 1;
            int t = 40;
            Graphics g = e.Graphics;
            foreach (Color c in colorList) {
                using (SolidBrush b = new SolidBrush(c)) {
                    g.FillRectangle(b, l, t, 30, 30);
                    l = l + 30;
                    if (l > 600)
                    {
                        l = 1;
                        t = t + 30;
                    }
                }
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            ColorDialog c = new ColorDialog();
            if (c.ShowDialog() == DialogResult.OK)
            {
                myColor = c.Color;
                getShadesAndTints(myColor);
                Invalidate();
            }
        }

        private void getShadesAndTints(Color c)
        {
            int i; Double m;
            int r; int g; int b;
            for (i = 1; i < 21; i++)
            {
                m = i * 0.1;
                r = (int)(c.R * m); if (r > 255) r = 255;
                g = (int)(c.G * m); if (g > 255) g = 255;
                b = (int)(c.B * m); if (b > 255) b = 255;
                colorList.Add(Color.FromArgb(r, g, b));
            }
        }

    }
}