CamVerce Studio: Object Editing: Colors and Lines tab
You can change fill color, line color and Transparency from Colors and Lines tab.
Fill color is the color inside of the object. If you want the object to be more transparent, move the slide to the right.
Line color will change the outside border color of the object. You can also change the style dashes and the line thickness.
The bottom section is only for Arrow objects and is disabled for other objects.