I love seeing the poly terrain in the background of screenshots, but the black horizon is less than appealing; could the sky extend all the way down the terrain?

If i move the horizon-line down, it gives the (cool but unwanted) impression that the minecraft-world is a sphere.

Is is possible to add a config option to lower this horizon line?

You can manually change the height here: SkyFragmentShader.js
You can also modify this value directly by searching for float horizonHeight = in /bluemap/web/js/app.cd4bf5d1.js

I got an email after 3 whole years holy shit

Since the creation of this issue BlueMap's render-distance is now much larger, meaning the horizon is less visible now. Additionally with #268 you will have the option to change the void-color to something else if you want.
For this reason I'll consider this issue solved and will close it.

Would like to see a config option to change the black color (per world preferably)
I have a floating islands world and I feel like it looks better colored instead of black

Current release:

Edited shaders to remove blackness (+ add fading to low res but thats not this issue):

could the sky extend all the way down the terrain?

It does, the terrain just does not render all the way to the horizon :D

Bluemap looks really weird if you watch if from above, top-down and there is a blue sky, that's why i added the skybox with a black void. If i move the horizon-line down, it gives the (cool but unwanted) impression that the minecraft-world is a sphere.

I will try blending out the black based on the camera-angle, but that might look weird as well, lets see ^^

+1