replace color in an image

using System.Drawing;

Color color = Color.Black; //Your desired colour

byte r = color.R; //For Red colour

Bitmap bmp = new Bitmap(this.BackgroundImage);
for (int x = 0; x < bmp.Width; x++)
{
    for (int y = 0; y < bmp.Height; y++)
    {
        Color gotColor = bmp.GetPixel(x, y);
        gotColor = Color.FromArgb(r, gotColor.G, gotColor.B);
        bmp.SetPixel(x, y, gotColor);
    }
}

Reference http://stackoverflow.com/questions/9871262/replace-color-in-an-image-in-c-sharp