A Color dialog box sends the COLOROKSTRING registered message to your hook procedure when the user selects a color and clicks the OK button. The hook procedure can accept the color and allow the dialog box to close, or reject the color and force the dialog box to remain open.
MessageID = RegisterWindowMessage(COLOROKSTRING);
wParam = 0;
lpcc = (LPCHOOSECOLOR) lParam;
If the hook procedure returns zero, the Color dialog box accepts the selected color and closes.
If the hook procedure returns a nonzero value, the Color dialog box rejects the selected color and remains open.
The hook procedure must specify the COLOROKSTRING constant in a call to the RegisterWindowMessage function to get the identifier for the message sent by the dialog box.