Logic Problem

Not that this matters a great deal, but you only need to bitwise-and with 0xffffff in one place:

Code:

private void CheckSelectFirework(Point point)
{
	foreach(Firework firework in Fireworks)
	{
		if(PointOverRect(point.X,
		                 point.Y, 
		                 firework.X, 
		                 firework.Y,
		                 FireworkTypes[firework.Angle][firework.Colour].Width,
		                 FireworkTypes[firework.Angle][firework.Colour].Height))
		{					
			foreach(Firework firework2 in Fireworks)
			{
				if(((LastColorSelected & firework.Colour.ToArgb()) & 0xffffff) == 0)
				{	
					firework2.IsSelected = false;
				}
			}
					
			firework.IsSelected = true;
			LastColorSelected = firework.Colour.ToArgb();
		}
	}
}

Thanks for all of your help!