The function prompt-for-color
pops up a dialog box allowing the user to choose a color.
message supplies a title for the dialog on GTK+ and Motif. On Microsoft Windows message is ignored.
color provides the default color in the dialog.
colors is a list of custom color specifications that the user can choose from.
owner specifies an owner window for the dialog. See Dialogs: Prompting for Input for details.
For a description of color specifications, see Color specs.
CAPI User Guide and Reference Manual (Unix version) - 3 Aug 2017