class ColorToGradient : ConverterBase
    {
        private Color MainColor { get; set; }
        public float Factor { get; set; } = -0.3f;

        public override object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            MainColor = value is Color color ? color : (Color)ColorConverter.ConvertFromString($"{value}");

            var secondColor = ChangeColorBrightness(MainColor, Factor);

            var stops = new GradientStopCollection
            {
                new GradientStop(MainColor, 0),
                new GradientStop(secondColor, 1)
            };

            return new LinearGradientBrush
            {
                StartPoint = new Point(.5, 0),
                EndPoint = new Point(.5, 1),
                GradientStops = stops
            };
        }

        private static Color ChangeColorBrightness(Color color, float correctionFactor)
        {
            float red = color.R;
            float green = color.G;
            float blue = color.B;

            if (correctionFactor < 0)
            {
                correctionFactor = 1 + correctionFactor;
                red *= correctionFactor;
                green *= correctionFactor;
                blue *= correctionFactor;
            }
            else
            {
                red = (255 - red) * correctionFactor + red;
                green = (255 - green) * correctionFactor + green;
                blue = (255 - blue) * correctionFactor + blue;
            }

            return Color.FromArgb(color.A, (byte)red, (byte)green, (byte)blue);
        }
    }