I am using WAB 2.4 and was very excited to see the Set Custom color in the styles. However what I have noticed is when you set your color it changes the apps title bar along with all of your widgets title bars but the buttons within the widgets stay the original color that was predefined, unlike the other color styles it changes the headers and the buttons. What .css changes the color of hover and selection in the widget buttons so it all matches, I'm having a hard time finding the location of where this color is being saved.
Custom Color Selected the title bars all changed, but the Search button on the widget is orange and the selected measure tool is orange.
With a pre-loaded color, the tittle bar all change along with all the buttons.