In Autodesk Revit dimensions are controlled per type (similar to style in AutoCAD). Therefore you cannot assign Background Mast to individual dimensions strings. You will need to create a separate Dimension Type which will have Backgrounds mask assigned to it. To do this:
- Highlight the dimension and under Properties Click “Edit Type”.
- In Type Properties click Duplicate and create copy of your current Text Styles, just append some identifier in the name – e.g. Masked.
- Under Text, Set Text Background to be Opaque (set it to be Translucent if you wish to remove background mask).