For that you have to download a custom palette, if you search a bit in google you will find it, then in the Retroarch directory inside the System folder you create a folder called Palettes, you put your custom palette in that folder and rename it to Default.pal, then when you run the core (in my case the Gambatte) you go to options and choose the custom option in GB colorization.
This is how I get my pea green palette from the original game boy.

I leave a capture of what I have achieved with the night mode, a custom palette and touching on the shader parameters, especially what is CRT Gamma, Brightness and green tone.
The capture looks a bit dark but live it looked very good and nothing dark.
For the night mode it is very easy, once you apply the desired preset you go to the shader parameters and look for the Night Lighting option, you raise it to 100 and you already have night mode .
