In version 2.0.17 fog was just fine.
I used this settings to get slightly dusty look in my world
https://imgur.com/a/4UlRn8A

client_default {
# This is used client-side (but only if the client has this mod) for the fog color [range: -1.0 ~ 1.0, default: -1.0]
S:fogBlue=0.59

# This is used client-side (but only if the client has this mod) for the fog density [range: -1.0 ~ 1.0, default: -1.0]
S:fogDensity=0.015

# This is used client-side (but only if the client has this mod) for the fog color [range: -1.0 ~ 1.0, default: -1.0]
S:fogGreen=0.79

# This is used client-side (but only if the client has this mod) for the fog color [range: -1.0 ~ 1.0, default: -1.0]
S:fogRed=0.92

# This is used client-side (but only if the client has this mod) to set the height of the horizon [range: -1.0 ~ 256.0, default: -1.0]
S:horizon=-1.0

}

But in version 2.0.18 i don't get any Fog doesnt matter what settings i use.

I see what happened. I will fix this

Fixed next release