WebInspector.Color.PageHighlight.Margin = WebInspector.Color.fromRGBA(255,0,0,0.8);
WebInspector.Color.PageHighlight.Content = WebInspector.Color.fromRGBA(0,255,0,0.8);
(Using the automatic code completion feature of the console, you can see the other properties you can change, like padding and similar. Just type WebInspector.Color. and it will show you the rest of the options)
5. Press Enter.
6. Try and highlight some element using the original Developer Tools window (that one that inspects the page). The margin will be red, the content will be green.
7. Close the second Developer Tools window, it is not needed anymore.
Once you close the original Developer Tools window, you will have to repeat this procedure to change the original colors again.
You can create a feature request at
crbug.com to convert this into a configurable user facing option within the Settings overlay, however, note the team may choose not to implement it (just so you know what to expect).