When a Measurement item is selected the SELECTION - TOOLS menu will be available. The SELECTION - TOOLS menu contains tools that allow you to change styling of the Measurement. The menu dynamically adjusts the tools available depending on your item selection 

Slope selection

Distance/Height selection
Styling group

LineAllows you to change the Measurement color.
LabelAllows you to change the label(s) color.
SizeAllows you to change the label(s) size.

SlopeAllows you to select the slope label style (ratio and/or slope). Only available when a slope item is selected.