Outline

Add an outline on all objects of the layer having the effect. This won't work well if shown on top of the background color of the scene. Be sure to use an object acting as a background or a floor.

Use Thickness to set how wide the outline is and Color to choose its color. This effect can also be applied to a single object instead of a whole layer, which is handy for highlighting a selected or hovered object.

Reference

All effects are listed in the effects reference page.