I’m not an expert by any stretch, but I’ve had a quick look – I guess you’ve tried the basic options within Tools > Options… ? Under ‘Environment’, there is UI Colour and in ‘Text Editor’ you can change the Colour Scheme or font. I just tried the Colour Scheme (e.g. dark), and the odd thing for me is Qt Creator just changes the colour scheme in the editing area and nowhere else (which is inconsistent). I’m using v3.