Does one need to configure something explicitly to have uplink nodes coloured in blue? For me all nodes still seem to be white in the topology view: https://map.luebeck.freifunk.net/meshviewer/#/en/graph/4c13650016e0

The installation should run on 585e05f.

No, this should not need something special.
You do need to have the gateways on the meshviewer though:
Take a look here: https://map.aachen.freifunk.net/#/en/graph

The helper function hasUplink looks at an existing linkType of type VPN..
How did hopglass do this instead?

Hopglass did create non-clickable nodes for the gateways.
Basically a shadow information as we know from the existing nodes, that there must be a gateway existing as well :D

I would rather fix this by installing mesh-announce on the gateways to get proper information..?
https://github.com/ffnord/mesh-announce