Invalid use of BPMN in Color in reference model C.1.0

[falko]

The reference model C.1.0 incorrectly uses color:background-color on bpmndi:BPMNLabel while it should use color:color.

In addition, the colors shown in the provided rendering don't seem to match the color codes in the XML.

See detailed discussion here: camunda/camunda-modeler#2452

[falko]

@davidgs FYI

[SimonRinguette]

As discussed on the 2021-10-13 meeting, a PR with these changes will be welcome