How do I make a CMFCToolBar recognize image masks?

Question

I have a CMFCToolBar-derived class and an insance thereof is the member of a CDockablePane-derived class.

I looked at the VisualStudioDemo sample to see how it's done and have this so far:

int CMyPane::OnCreate(LPCREATESTRUCT lpCreateStruct)
{
    // Removed all "return -1 on error" code for better readability

    CDockablePane::OnCreate(lpCreateStruct);

    if(m_toolBar.Create(this, AFX_DEFAULT_TOOLBAR_STYLE, IDR_MY_TOOLBAR) &&
       m_toolBar.LoadToolBar(IDR_MY_TOOLBAR, 0, 0, TRUE /* Is locked */))
    {

        if(theApp.m_bHiColorIcons) // Is true, i.e. following code is executed
        {
            m_toolBar.CleanUpLockedImages();
            m_toolBar.LoadBitmap(IDB_MY_TOOLBAR_24, 0, 0, TRUE /*Locked*/);
        }

        m_toolBar.SetPaneStyle(m_toolBar.GetPaneStyle() | CBRS_TOOLTIPS | CBRS_FLYBY);
        m_toolBar.SetPaneStyle(m_toolBar.GetPaneStyle() & ~(CBRS_GRIPPER | CBRS_SIZE_DYNAMIC | CBRS_BORDER_TOP | CBRS_BORDER_BOTTOM | CBRS_BORDER_LEFT | CBRS_BORDER_RIGHT));

        m_toolBar.SetOwner(this);

        // All commands will be routed via this control , not via the parent frame:
        m_toolBar.SetRouteCommandsViaFrame(FALSE);
    }

    return 0;
}

The high-color image (24bit) is loaded but the magenta mask (R255 G0 B255) is visible. I don't see how I can tell the toolbar to recognize the mask.
Is this even possible?

Answer 1

I just found out that a workaround is to use 32bit images together with their alpha channel. I tried using a 32bit image earlier but didn't get it to work for some other reason and then figured 32bit images won't work.

Answer 2

I don't know if this works every time but I use RGB(192, 192, 192) as the mask color and it does get recognized.

(Seems like the CMFCToolBar control is prepared to use ::GetSysColor(COLOR_BTNFACE) as the transparent color...)