Is there any way for a tooltip to show the selected colour descriptively?

It is possible to configure the CMFCColorDialog to how the active colour in a tooltip when the mouse is over it?

Being colour blind I find it hard to identify "Red" for example. I got around it by clicking the Custom tab and using the RGB properties and setting Red that way:

But I wondered if a tooltip could be supported.

I didn't find any built-in functionality supporting tooltips here.

But, if you are open to DIY project ( and I feel that you are ), you can easily subclass that dialog, overriding single PreTranslateMessage function:

#pragma once
#include <afxcolordialog.h>
class CMyColorDlg :
    public CMFCColorDialog
{
public:
    virtual BOOL PreTranslateMessage(MSG* pMsg);
private:
    CToolTipCtrl m_ToolTip;
    bool m_bCreate = true;
    bool m_bTrackingMouseLeave = false;
    COLORREF m_LastColor = 0;
};

Here is my demo implementation:

#include "pch.h"
#include "CMyColorDlg.h"

BOOL CMyColorDlg::PreTranslateMessage(MSG* pMsg) {
	if (pMsg->message == WM_MOUSEMOVE) {
		if (m_bCreate) {
			m_bCreate = false;
			m_ToolTip.Create(&m_pColourSheetOne->m_hexpicker, TTS_ALWAYSTIP | TTS_NOANIMATE);
			m_ToolTip.AddTool(&m_pColourSheetOne->m_hexpicker, L"RGB");
		}
		CWnd* pw = WindowFromPoint(pMsg->pt);
		if (pw->m_hWnd == m_pColourSheetOne->m_hexpicker.m_hWnd) {
			if (!m_bTrackingMouseLeave)
			{
				TRACKMOUSEEVENT tme = { 0 };
				tme.cbSize = sizeof(TRACKMOUSEEVENT);
				tme.dwFlags = TME_LEAVE;
				tme.hwndTrack = m_hWnd;
				::_TrackMouseEvent(&tme);

				m_ToolTip.Activate(TRUE);
				m_bTrackingMouseLeave = TRUE;
			}
			pw->ScreenToClient(&pMsg->pt);
			COLORREF color = pw->GetDC()->GetPixel(pMsg->pt);
			if (m_LastColor != color) {
				if (color == 0xF9F9F9) { // RGB(249,249,249) - gray around the color stuff
					m_ToolTip.Activate(FALSE);
				}
				else if (m_LastColor == 0xF9F9F9) {
					m_ToolTip.Activate(TRUE);
				}
				m_LastColor = color;
				CString s;
				s.Format(L"R=%d, G=%d, B=%d\n",
					GetRValue(color), GetGValue(color), GetBValue(color));
				m_ToolTip.UpdateTipText(s, &m_pColourSheetOne->m_hexpicker);
				m_ToolTip.Popup();

			}
		}
	}
	else if (pMsg->message == WM_MOUSELEAVE) {
		m_bTrackingMouseLeave = FALSE;
		m_ToolTip.Activate(FALSE);
	}

	return CMFCColorDialog::PreTranslateMessage(pMsg);
}

You only get WM_MOUSEMOVE over that control after you click <kbd>Select...</kbd> button.

UPDATE:

With a credit to Ovidiu Cucu, added tracking tooltip control.