In the field at the bottom right you can assign pens, styles and halos to the dimension arrows and leader lines.

In the pen, style and halo dialog boxes, you can choose any options from the selection provided. Any additional pens, styles and halos that have been created are included in the current document.

The setting for the leader lines applies for the dimension leader lines.

The Start arrow and End arrow settings apply for the dimension arrows, their starts and their ends.