This appears as a thick line around an item when the mouse is over it. The default hover color is pure blue, but this may be changed via the settings panel . Objects and pins are hovered seperately. Objects with controls have a seperate inner hover. Hovered items also recieve keystrokes.
Most objects have a complete set of hot-keys.
See Objects for details. There are two workspace modes, each having a different background color . Switch between modes using the tab key, a popup menu, or the shift key. Mouse operation and File Dropping operate differently for the two modes. Normal mode Gray by default.