The way that the Colour Settings are selected is as follows:
-- for each style, there are at least 8 colour presets in the Root folder (click [Presets] in the Colour setitngs window to see them,
-- depending of the plug-in type (Dynamics, Reverb, EQ etc) a different one of the 8 is selected
-- the fifth colour in each preset (Inactive Window Overlay) is not defined in these presets so the fourth colour (Highlights) is used, with an alpha value of 0; to get the feature to work, edit the fifth colour and drag its alpha value up.
-- that plug-in is an EQ, so, by default, the second preset (green tones) will be selected.
-- distortion-type plug-ins would use the fifth preset (red tones).
Here is the screenshot of the colour presets for Ozone here:

-- I have indicated the 8 defaults and the one selected for EQs,
-- you will also see that I am building up my own colour presets,
-- as a reminder I have added a "zz Default Categories" folder, with sub-folders named after each plug-in type and their associated colour tone (and an extra one - yellow)
Once you get the hang of how these colours work, the system is very powerful (but it does depend on the Style being used).
Hope that that helps
