Most objects that occupy a two-dimensional area (polygons, circle interiors, arc interiors, pictures, iterations and loci of these objects, and angle markers) have adjustable opacity, so that they can allow similar objects in layers below them to show through.
The opacity scale goes from 0% (completely transparent) to 100% (completely opaque).
When you create pictures, iterated pictures, and loci they are initially opaque, with an opacity of 100%.
When you create polygons, circle interiors and arc interiors they are initially translucent, with an opacity of 50%.
To change the opacity of a translucent object, select it and choose Edit | Properties | Opacity.
For most objects, the minimum opacity value is 10%, so that you cannot set them to be completely transparent. (A completely transparent object would be invisible.)
Framed polygons and angle markers are the only objects that can be made completely transparent.
•Polygons have an optional frame in addition to their interiors. If a polygon’s frame is showing, you can set its opacity to 0% to show only its frame.
•Angle markers have one or more strokes in addition to their filled areas. You can set an angle marker’s opacity to 0% to show only its strokes(s).
Most translucent objects are also layered objects, and can be arranged above or below other similar objects by using Bring to Front or Send to Back from the object’s Context menu. The only exceptions are angle markers, which are always visible above other layered objects.