Thanks! I was thinking you used an outline shader (it does look pretty obvious), but since I never really dipped my toes into shaders, I have no idea how to properly use them. The site you linked does look really informative, I'll definitely check that out :) Oh, and the color palette works wonders, you're right.
Personally, I always focus waaaaayy too much on the programming part and leave the visual stuff for the last few hours, which I really need to improve on as I never have enough time to achieve the look I have in my head.
Thanks for your answer! :)