Progress bar enables to assign different colours to background –the one of the bar acting as an indicator of the full length of the video– and to progress –the portion of video consumed over total–. You can modify such parameters from the General submenu, which are shown in black by default in both cases.
The Progress bar addon enables the preference of the button level of visibility through the control of opacity in design. On the General submenu, click on the option Show opacity to display the opacity parameters. Choose a value between 0 and 1, where 0 means 0% visibility, 1 is 100% and 0.5 corresponds to 50% visibility. The values to modify are BG for Background and PG for Progress. This parameter is not related to background colour or progress colour.
Another possibility available for the Progress bar addon is to show markers with the position of interactivities on the video. If you choose the option Visible on the Markers parameter of the General submenu, your progress bar will show the points of the video in which there are interactive elements. This is information you may decide not to give to users, which is why it is disabled by default.