Each XL toolhead is equipped with a Dwarf board, and a status LED with several possible colors. Below is an explanation of the meaning of each color.
Blue
The Dwarf is in a "bootloader", inactive state. It is not communicating yet with the main XLBuddy board, but is waiting for communication to be established, either finishing start-up or finishing a firmware upgrade.
Green
The Dwarf is in a regular, but inactive state. The application on the Dwarf is running, communicating with the main XLBuddy board.
White
The tool is in an active state. Only one tool can be active at a given moment.
Yellow
Regularly, a tool can be either picked or parked. A yellow LED indicates that the tool is neither picked nor parked. This status typically indicates mechanical or electrical problems with a wrongly parked or picked tool.
Red
The tool has an error, its application crashed. It is possible that an error on this would propagate to the main XLBuddy board, rendering the status Blue.