The COLOROKSTRING message is sent by the Color dialog box to the application's hook function immediately before the dialog box is closed. This message allows more control over custom colors by giving the application the opportunity to leave the Color dialog box open when the user presses the OK button.
wParam
Not used.
lParam
Points to a CHOOSECOLOR structure that specifies the currently selected color.
If the application returns a nonzero value when it processes this message, the dialog box is not dismissed.
To use this message, the application must create a new message identifier by calling the RegisterWindowMessage function and passing the COLOROKSTRING constant as the single parameter.