private System.Drawing.SolidBrush InterpolateBrush(System.Drawing.Brush min, System.Drawing.Brush max, double attr)
{
if (min.GetType() != typeof(System.Drawing.SolidBrush) || max.GetType() != typeof(System.Drawing.SolidBrush))
throw (new ArgumentException("Only SolidBrush brushes are supported in GradientTheme"));
return new System.Drawing.SolidBrush(InterpolateColor((min as System.Drawing.SolidBrush).Color, (max as System.Drawing.SolidBrush).Color, attr));
}