If you want bar numbers to stand out, you can enclose them in a rectangular or circular enclosure. You can change the bar number enclosure type in each layout independently of other layouts.
For example, you can have bar numbers appear with rectangle enclosures in full score layouts but with no enclosures in part layouts.
Procedure
Press Ctrl/Cmd-Shift-L to open Layout Options.
In the Layouts list, select the layouts in which you want to change the bar number enclosure type.
By default, the layout currently open in the music area is selected when you open the dialog. You can select other layouts by using the selection options in the action bar, Shift-clicking adjacent layouts, and Ctrl/Cmd-clicking individual layouts.
Click Bar Numbers in the page list.
In the Appearance subsection, choose one of the following options for Enclosure type:
None
Rectangle
Circle
Click Apply, then Close.
Result
Bar numbers in the selected layouts are shown within your selected enclosure type. The size of the enclosure is relative to the font size of the bar numbers, but the size and shape of the enclosure are also determined by your padding values.