Went around the internets to find the one I thought of and while I can't find it - doesn't surprise me - it was something very much like a cross between Denshi Block (connectors) and Braun Lectron (aesthetics)

https://de.wikipedia.org/wiki/Lectron

Gakken made Denshi variants, including one that looks a bit like the Lectron for students in Japan:

https://www.petervis.com/electronics-lab/denshi-block-series...

And:

https://axel.as-1.co.jp/asone/maker/MH17083/

I like the readability of those.