IMenuStripColorTable

Implement it on a class that derives from ProfessionalColorTable - the menu needs both: the base class for backgrounds, borders, the image margin and the highlight behind the item under the pointer, and this interface for what is drawn on top of them. Pass an instance to the ExtendedContextMenuStrip() constructor, or to a control that takes one, such as the smart button's MenuStripColorTable.

"Selected" means the item under the pointer or chosen with the arrow keys.

public sealed class HighContrastMenuColours : ProfessionalColorTable, IMenuStripColorTable
{
    public override Color ToolStripDropDownBackground => Color.Black;
    public override Color ImageMarginGradientBegin => Color.Black;
    public override Color ImageMarginGradientMiddle => Color.Black;
    public override Color ImageMarginGradientEnd => Color.Black;
    public override Color MenuItemSelected => Color.Yellow;

    public Color ArrowColor => Color.Yellow;
    public Color ArrowColorWhenItemSelected => Color.Black;
    public Color MenuItemTextColor => Color.White;
    public Color MenuItemTextColorWhenItemSelected => Color.Black;
    public ArrowKind ArrowRenderingStyle => ArrowKind.Thick;
}