Code for setting the active selection to use a gradient brush, like beta 1 (VS 2010 Beta 2).

SetGradientBrush.cs

void SetGradientBrush(IEditorFormatMap formatMap)
{
    Color highlight = SystemColors.HighlightColor;
    Color darkColor = Color.FromArgb(96, highlight.R, highlight.G, highlight.B);
    Color lightColor = Color.FromArgb(48, highlight.R, highlight.G, highlight.B);

    // Change the selected text properties to use a gradient brush and an outline pen
    var properties = formatMap.GetProperties("Selected Text");
    properties[EditorFormatDefinition.BackgroundBrushId] = new LinearGradientBrush(
        new GradientStopCollection() { new GradientStop(darkColor, 0.0), new GradientStop(lightColor, 0.5), new GradientStop(darkColor, 1.0) }, 90.0);
    properties["BackgroundPen"] = new Pen(SystemColors.HighlightBrush, 1) { LineJoin = PenLineJoin.Round };
    formatMap.SetProperties("Selected Text", properties);
}