Is this when you select a particular object, or any?

Draw a rectangle
Open the Colour Editor
In the drop down menu at the top you'll have 'Local line colour' and 'Local fill colour'.

You can also apply a line colour by first selecting the object and applying a line width from the drop down menu at the top of the program window, then chnage it's colour by right clicking on a colour from the colour line at the bottom and select 'Set line colour'