It’s possible to disable the blueprint/material grids by disabling Use Grids In The Material And Blueprint Editor option in Editor Preferences - Appearance - Graphs. Is it possible to disable the UMG grid somehow? I would like to see a flat color in the background like in the blueprint/material editors.
You can asign the false value to bDrawGridLines in SdesignSurface::Construct function to disable grid lines in UMG BP