From Xojo Documentation
Displays the system Color Picker, allowing the user to choose a color.
|result||Boolean||Returns True if the user clicks OK; False if the user cancels.|
|col||Color||Color passed to SelectColor and the color the user selects.
Note the usage of ByRef in the parameter list.
|prompt||String||Prompt to be displayed in the Color Picker. Shown only on Linux.|
|showAlpha||Boolean||Shows alpha opacity in the Color Picker. Only for macOS. Defaults to False.|
You control the default choice of color displayed by the Color Picker by passing a value of col to SelectColor. If col is not assigned a value, black is used as the default color. The color that the user chooses is returned in col. If the user clicks Cancel without making a choice, result is set to False; otherwise it is set to True.
The following example allows the user to select a color that will be used as the fillcolor in a Rectangle control.
Var b As Boolean
c = Color.CMY(0.35, 0.9, 0.6, 0) // choose the default color shown in color picker
b = Color.SelectedFromDialog(c, "Select a Color")
Rectangle1.FillColor = c
If you don't want to test the boolean returned by SelectedFromDialog, you can call it using Call.