Haha yeah the colors are a bit messy and hard to read. I've touched things a bit for the one I'm developing right now (not the next public).
For the buttons it didn't really bother me since I always choose with the mouse and it's obvious, but when choosing with keys it might be difficult to differentiate.
The engine (Godot) is not a visual novel one, it's a generalist one. I have to code everything (which I enjoy!), like the dialogue system. The conversation history will be included eventually, of course.
The fullscreen is included in the next public already, but I still have to make different resolutions options.