When you insert a new shape on a slide in PowerPoint 2016 (or in any previous version), by default it is filled with a solid color and an outline (or something else depending on the Theme your presentation is based on). For example in a new blank presentation that we created, the shape is by default filled with a blue solid fill and has a thin dark blue outline. Whenever we insert another new shape on a slide, it will possess these same default shape attributes (fill, outline, and effect).
Change default shape attributes in PowerPoint 2016 for Windows.

