How to remove custom color settings

I wanted the primary menu bar to have a transparent background so I went to theme settings and tried to change "Color Options" -> "Primary Menu Color Options" -> "Menu Background Color" to "transparent" ... BUT, the theme does not allow it... So i changed the colour a few times but just wasn't happy so I then went and changed it manually in the child-tmeme/style.css file. The problem is that since I changed the background color once, it has permanently set the theme to write the background css into the theme as an in-page style in the header. What I have found: Default styles appear in style.css BUT If you change from default, it writes the new style in the header BELOW the style.css AND child-theme/style.css ... Therefore, any change I make in child-theme/style.css is overwritten by the in-page styles... PLUS - to make it worse, even if I go back into the "Customise" section of the theme and change the colour back to "default" - it doesn't remove the in-page style BUT instead, it just writes the same in-page style with the same "default" colour, creating a superfluous style... How can I remove this so that the backend/style for a specific colour section ("Menu Background Color") no longer writes into the in-page header and just uses the default style? How do I reset/remove that one style from the in-page styles? I really don't want to start using !important to force overwrite in-page styles...