ProgressBar.cs

namespace CurePlease
{
    using System.Drawing;
    using System.Drawing.Drawing2D;
    using System.Windows.Forms;

    public class NewProgressBar : ProgressBar
    {
        public NewProgressBar() => this.SetStyle(ControlStyles.UserPaint, true);

        protected override void OnPaintBackground(PaintEventArgs e)
        {
            if (this.ClientRectangle.Width > 0 && this.ClientRectangle.Height > 0)
            {

            }
        }
        protected override void OnPaint(PaintEventArgs e)
        {
            const int inset = 2; // A single inset value to control teh sizing of the inner rect.

            using (Image offscreenImage = new Bitmap(this.Width, this.Height))
            {
                using (Graphics offscreen = Graphics.FromImage(offscreenImage))
                {
                    Rectangle rect = new Rectangle(0, 0, this.Width, this.Height);

                    if (ProgressBarRenderer.IsSupported)
                        ProgressBarRenderer.DrawHorizontalBar(offscreen, rect);

                    rect.Inflate(new Size(-inset, -inset)); // Deflate inner rect.
                    rect.Width = (int)(rect.Width * ((double)this.Value / this.Maximum));

                    if (rect.Width != 0)
                    {
                        LinearGradientBrush brush = new LinearGradientBrush(rect, ForeColor, ForeColor, LinearGradientMode.Vertical);
                        offscreen.FillRectangle(brush, inset, inset, rect.Width, rect.Height);
                        e.Graphics.DrawImage(offscreenImage, 0, 0);
                        offscreenImage.Dispose();

                    }
                    else
                    {
                        rect.Width = 215;

                        LinearGradientBrush brush = new LinearGradientBrush(rect, SystemColors.ScrollBar, SystemColors.ScrollBar, LinearGradientMode.Vertical);
                        offscreen.FillRectangle(brush, inset, inset, rect.Width, rect.Height);
                        e.Graphics.DrawImage(offscreenImage, 0, 0);
                        offscreenImage.Dispose();

                    }
                }
            }
        }
    }
}

// Source: http://stackoverflow.com/questions/778678/how-to-change-the-color-of-progressbar-in-c-sharp-net-3-5