I really want to add an onhover color . Whenever I move my cursor over a menu item , the selected item's background should change, for example if the color of the menu bar is grey , then onhover of the menu item, the background color specific to the menu item should change to some other color say green . And If I click to the item, the changed color green should persist and rest items should stay grey .If I click other menu item, color of the previously selected color should go from green to grey and currently selected should be green.Hope I am able explain my question.
This can all be achieved using CSS and SASS. Here you can find a (old, bit still acurate) blog describing how this works and can be achieved: https://www.mxblog.nl/2016/03/using-sass-with-mendix/
Here is some information to get you started for your specific needs: https://stackoverflow.com/questions/19914926/css-menu-hover-text-colour
I believe you can create a costum theme for yourself that contains the described behaviour.
This should be relatively easy to do with the mendix theme creator: