Changing Color Tint with C#

ColorExtensions.cs

public static class ColorExtensions
{
    /// <summary>
    /// Tints the color by the given percent.
    /// </summary>
    /// <param name="color">The color being tinted.</param>
    /// <param name="percent">The percent to tint. Ex: 0.1 will make the color 10% lighter.</param>
    /// <returns>The new tinted color.</returns>
    public static Color Lighten( this Color color, float percent )
    {
        var lighting = color.GetBrightness();
        lighting = lighting + lighting * percent;
        if( lighting > 1.0 )
        {
            lighting = 1;
        }
        else if( lighting <= 0 )
        {
            lighting = 0.1f;
        }
        var tintedColor = ColorHelper.FromHsl( color.A, color.GetHue(), color.GetSaturation(), lighting );

        return tintedColor;
    }

    /// <summary>
    /// Tints the color by the given percent.
    /// </summary>
    /// <param name="color">The color being tinted.</param>
    /// <param name="percent">The percent to tint. Ex: 0.1 will make the color 10% darker.</param>
    /// <returns>The new tinted color.</returns>
    public static Color Darken( this Color color, float percent )
    {
        var lighting = color.GetBrightness();
        lighting = lighting - lighting * percent;
        if( lighting > 1.0 )
        {
            lighting = 1;
        }
        else if( lighting <= 0 )
        {
            lighting = 0;
        }
        var tintedColor = ColorHelper.FromHsl( color.A, color.GetHue(), color.GetSaturation(), lighting );

        return tintedColor;
    }
}

ColorHelper.cs

public static class ColorHelper
{
    /// <summary>
    /// Converts the HSL values to a Color.
    /// </summary>
    /// <param name="alpha">The alpha.</param>
    /// <param name="hue">The hue.</param>
    /// <param name="saturation">The saturation.</param>
    /// <param name="lighting">The lighting.</param>
    /// <returns></returns>
    public static Color FromHsl( int alpha, float hue, float saturation, float lighting )
    {
        if( 0 > alpha || 255 < alpha )
        {
            throw new ArgumentOutOfRangeException( "alpha" );
        }
        if( 0f > hue || 360f < hue )
        {
            throw new ArgumentOutOfRangeException( "hue" );
        }
        if( 0f > saturation || 1f < saturation )
        {
            throw new ArgumentOutOfRangeException( "saturation" );
        }
        if( 0f > lighting || 1f < lighting )
        {
            throw new ArgumentOutOfRangeException( "lighting" );
        }

        if( 0 == saturation )
        {
            return Color.FromArgb( alpha, Convert.ToInt32( lighting * 255 ), Convert.ToInt32( lighting * 255 ), Convert.ToInt32( lighting * 255 ) );
        }

        float fMax, fMid, fMin;
        int iSextant, iMax, iMid, iMin;

        if( 0.5 < lighting )
        {
            fMax = lighting - ( lighting * saturation ) + saturation;
            fMin = lighting + ( lighting * saturation ) - saturation;
        }
        else
        {
            fMax = lighting + ( lighting * saturation );
            fMin = lighting - ( lighting * saturation );
        }

        iSextant = (int)Math.Floor( hue / 60f );
        if( 300f <= hue )
        {
            hue -= 360f;
        }
        hue /= 60f;
        hue -= 2f * (float)Math.Floor( ( ( iSextant + 1f ) % 6f ) / 2f );
        if( 0 == iSextant % 2 )
        {
            fMid = hue * ( fMax - fMin ) + fMin;
        }
        else
        {
            fMid = fMin - hue * ( fMax - fMin );
        }

        iMax = Convert.ToInt32( fMax * 255 );
        iMid = Convert.ToInt32( fMid * 255 );
        iMin = Convert.ToInt32( fMin * 255 );

        switch( iSextant )
        {
            case 1:
                return Color.FromArgb( alpha, iMid, iMax, iMin );
            case 2:
                return Color.FromArgb( alpha, iMin, iMax, iMid );
            case 3:
                return Color.FromArgb( alpha, iMin, iMid, iMax );
            case 4:
                return Color.FromArgb( alpha, iMid, iMin, iMax );
            case 5:
                return Color.FromArgb( alpha, iMax, iMin, iMid );
            default:
                return Color.FromArgb( alpha, iMax, iMid, iMin );
        }
    }
}