How to change default styles
1.) Start with the artboard you want to add an overlay or measurement to.
2.) Add an overlay or measurement if there isn't one already. In this case I applied a spacing measurement.
3.) In the spacing measurement layer, select the parts (either background or text) that you want to change styles for. This is easiest when done in the layers panel on the left of Sketch.
4.) Look at the properties for the selected elements. You'll see that a default Sketch shared style is applied, in this case "@Spacing / Layer". This is shared style that Measure applies by default to all spacing measurement background layers.
5.) We want to change the spacing measurement background color so let's select that.
6.) The shared style now has a "refresh" icon next to it because it has been changed. Click it to apply the new color to the shared style, which will effect all elements using this shared style (and all new spacing measurements because we're changing the default shared style "@Spacing / Layer").
7.) Now our spacing measurement has an updated background color. New spacing measurements will have this new color because we applied it to the shared style.
You don't have to edit the default shared style. Instead you could create a new shared style, apply a fill to it, and be more choosy about what shared styles you apply to what layers.
Hope this was helpful!
- Jered