When you set a background color for a style, it should appear in the Styles dropdown. It worked in 4.2 (Regression).
I will look, now
Only has implement the Style "Color" the others "gradient, hatching and bitmap" ignore. gerrit: https://gerrit.libreoffice.org/#/c/11762/
http://cgit.freedesktop.org/libreoffice/core/commit/?id=dc358107b88badba60bc348564034ac2ad19c65c