The SETRGBSTRING message is sent by an application's hook function to a Color dialog box to set a custom color.
wParam
Not used.
lParam
Specifies the color to set. This parameter must be a red, green, blue (RGB) value.
This message has no return value.
To use the SETRGBSTRING message, the application must create a message identifier by using the RegisterWindowMessage function and passing the SETRGBSTRING constant as the function's single parameter.