How do I change the basemap opacity?

[LR2]

I need to change the transparency of the basemap, but there's no option in the UI and neither appending a parameter to the URL nor trying to edit the MapComponent in C++ got me anywhere. How do I do this?

(mind that I just started using Unreal, so you can't be too detailed 😏)

[MichaelBranscomb]

Can share any more info about why you want to change the opacity of the basemap? (e.g. for greater contrast with your own overlaid content, to see content beneath the basemap, to see content beneath the terrain/surface...)

The Basemap is a collection of ArcGISLayers, so you could write code to iterate the layers in the collection and set the opacity. Or alternatively, add the layers that you want as your basemap as regular layers via the UI where you can then set the opacity (and remember to set the API key / authentication type). 

The basemaps in the gallery are effectively the basemaps included in the (for developers) group on ArcGIS.com: 

• Group: Developer basemaps-api - Overview (arcgis.com)
• Example basemap item: https://www.arcgis.com/home/item.html?id=4094f2a1c7e5466f8d8d5a18f077e16a 

Those services all require a "token" - for more info see access token | Documentation | ArcGIS Developers