Picking an appearance in Form settings changed only your working copy of the form. The published form kept its old look until you went back to the editor and published again, with no indication that anything was outstanding.
Worse, publishing to apply a colour change also took live whatever else was sitting unpublished in that form — half-finished questions included.
Appearance is now separate from the published version of a form. Choosing one applies to the live form immediately, and it no longer publishes anything else along with it.