Is it possible to adjust the color of the hook in a checked RadCheckBox?

Thanks, this worked.

One minor issue left: while the hook looks centered, the indeterminate square is slightly off-centered.

Either it is 1 pixel too small to the right and bottom -or- it is one pixel too large to the top and left.

How could this be fixed?

Thank you for the provided image.

This could happen if you show the form on a HDPI. Can you share what is the DPI on the monitor where the form is shown?

On my LG UltraGear 34GK950G-B the pixels per inch are 110 with the default resolution of 3440x1440 and I do not use any scaling.

Update:

By using NativeMethods.GetSystemDpi(); I get a Point of (96; 96).

Fixed it:

First, I tried to manually paint a Bitmap and use it as Image but the problem is that your code somehow automatically tries to scale it and fails (e.g. it widened an 8x8 image to 13x13 pixels here which looked rather bad). As I did not find any setting to disable the automatic scaling I finally solved it by painting the square directly.

1. Switch the CheckPrimitiveStyle property depending on the CheckState in order to only paint the checked hook but not the indeterminate square:

protected override void OnCheckStateChanged(EventArgs e) {
  base.OnCheckStateChanged(e);

  if (CheckState == CheckState.Checked) {
    ButtonElement.CheckMarkPrimitive.CheckElement.CheckPrimitiveStyle = CheckPrimitiveStyleEnum.Win8;
  } else {
    ButtonElement.CheckMarkPrimitive.CheckElement.CheckPrimitiveStyle = CheckPrimitiveStyleEnum.None;
  }
}

protected override void OnLoad(Size desiredSize) {
  base.OnLoad(desiredSize);

  if (CheckState == CheckState.Checked) {
    ButtonElement.CheckMarkPrimitive.CheckElement.CheckPrimitiveStyle = CheckPrimitiveStyleEnum.Win8;
  } else {
    ButtonElement.CheckMarkPrimitive.CheckElement.CheckPrimitiveStyle = CheckPrimitiveStyleEnum.None;
  }
}

2. Paint the indeterminate square manually by overriding OnPaint():

protected override void OnPaint(PaintEventArgs e) {
  base.OnPaint(e);

  if (CheckState == CheckState.Indeterminate) {
    using Brush brush = new SolidBrush(Color.Aqua);

    GraphicsState gstate = e.Graphics.Save();
    e.Graphics.FillRectangle(
      brush,
      ButtonElement.CheckMarkPrimitive.ControlBoundingRectangle.Location.X + 5,
      ButtonElement.CheckMarkPrimitive.ControlBoundingRectangle.Location.Y + 5,
      ButtonElement.CheckMarkPrimitive.ControlBoundingRectangle.Size.Width  - 10,
      ButtonElement.CheckMarkPrimitive.ControlBoundingRectangle.Size.Height - 10
    );
    e.Graphics.Restore(gstate);
  }
}

The size & location of the painted rectangle depends on the CheckMarkPrimitive, its border(s) and the padding you want to apply. As all my borders have a width of 1 pixel and I wanted a padding of 4 pixels the sum of the space is 5. The width and height should then be subtracted by the double of this amount in order to place the square in the centre of the CheckMarkPrimitive.

Hi Dinko,

the base theme used is Fluent.Dark but I do not want to adjust the color(s) via the theme (which means the Visual Style Builder) but programmatically. Do I need to override some OnPaint()?