I've concluded a simple explanation for the horizon on a flat earth is that it is just a mirage. If you see those pictures of the desssert road with patches of shimmreing mirror on them - what color is the mirror - it is reflecting the sky and is the same color as the sky.
This is what i think happens at the horizon.
i have recently heard it said, and take it as truth, that the ground ramps up when looking straight to the vanishing point, and this is not because you are looking down somewhat - it is actually an effect not described in science - the ramping up of the ground to the vanishing point.
I am pretty sure youtuber "Mr thrive and survive" talks about this ramping up of the foreground, but to what extent i am not sure.
This video shows the horizon out to sea with floating waves above the horizon potentially demonstrating this idea that the horizon is a mirror.