enable left vertical side bar to be assigned a color to enhance visual indentification

[ReesePlews]

the original Plateau HTML deliverables used color to differentiate between documents 1 and 2. with the new viewer the color is the same, so when multiple windows are open, even though the title is present in the left vertical bar, they cannot be quickly differentiated visually because the color is the same.

please consider a simple way that the color of the left vertical side bar can be changed.

the left vertical side bar (in my understanding) is the area shown in green on the image below: