Instead of working on gameplay stuff I went on to fiddle with colors. Blame it on the christmas :)
I really like the pure monochrome look. It has a mysterious x-ray feel to it. However adding more color can broaden the variety of generator output and maybe get better emotional response from the player.
I'm keeping with the approach of having one vivid dominant color, but have added a secondary varying color for the sea (plus the hue shifts caused by tinted ambient added earlier). This will hopefully result in some pleasant color combinations.
I must say that Godot's Color object is pretty simple and not really suited for color manipulation. So I had to write a basic YUV class that converts from/to rgb and handles some common color transformations, like hue and saturation shifts. Luckily, rgb-yuv conversion is rather simple (just a linear transformation). I think Godot should natively have some support for color spaces that are more intuitive to work with for humans than rgb.
Two pairs of screenies below showing variations with the same dominant color. I might go with even stronger hue/saturation shifts than this.
Main color yellow/orange:


Main color magenta:

