Regenbogen

The German surname is a topographic or habitational name for someone who in a house with a rainbow and the Jewish usage is ornamental. [noted -ed]
Check the websites
https://www.ancestry.com/name-origin?surname=regenbogen
https://www.igenea.com/en/surnames/r/regenbogen
https://www.familysearch.org/en/surname?surname=Regenbogen
https://forebears.io/surnames/regenbogen
https://en.m.wikipedia.org/wiki/Regenbogen