Theme settings in SAP Collaboration Hub only change the theme in HUB, in SPM/SPG/SPI, the theme is not customizable.
This idea hasn't been implemented, and has been forwarded to our Product Managers as a Feature Request.
If you like this idea, please register your interest by creating a ticket in the SAP Signavio Support portal, referencing this knowledge base article.
We'd also like your business case, so we can better understand the needs of our customers.
KBA , BPI-SIG-PG-EDT , Process Governance Editor , Product Enhancement