The Color dialog box has a basic version and an extended version. The basic version has controls that display the basic and custom colors from which the user can select. The extended version includes the basic controls and has additional controls that allow the user to create custom colors.
The basic version of the Color dialog box includes a Define Custom Colors button. The user can click this button to display the extended version. You can direct the Color dialog box to always display this extension by setting the CC_FULLOPEN flag in the Flags member of the CHOOSECOLOR structure. To prevent the user from creating custom colors, you can set the CC_PREVENTFULLOPEN flag to disable the Define Custom Colors button.
The basic colors represent a selection of the colors available on the given device. The actual number of colors displayed is determined by the display driver. For example, a VGA driver displays 48 colors, and a monochrome display driver displays only 16.
The custom colors are those that you specify or that the user creates. When you create a Color dialog box, you must use the lpCustColors member of the CHOOSECOLOR structure to specify the initial values for the 16 custom colors. If the extended version of the Color dialog box is open, the user can create a custom color by one the following methods:
To add a new custom color to the custom colors display, the user can click the Add to Custom Colors button. This also causes the dialog box to copy the RGB value of the new color to the corresponding element in the array pointed to by the lpCustColors member. To preserve new custom colors between calls to ChooseColor, you should allocate static memory for the array. For more information about the RGB and HSL color models, see Color Models Used by the Color Dialog Box.