I'm having a weird problem. When I start ngrok, the terminal gets an orange background. The background returns to normal when I stop ngrok.
I'm running fish shell, in tmux, on ubuntu 16.04, over ssh, via cygwin terminal. Hope this helps...

Sorry, I should've minimized the reproduction steps. The issue also occurs on bash, without tmux.
My ngrok version is 2.2.8
I found out that the issue occurs when base16-shell theme is active. Does this help?
I had this problem too on Arch, using Zsh and Base16-shell.
I solved this problem by setting console_ui_color: transparent on ~/.ngrok2/ngrok.yml file.
Thanks, it works! I had to manually create the file though.
Most helpful comment
I had this problem too on Arch, using Zsh and Base16-shell.
I solved this problem by setting
console_ui_color: transparenton~/.ngrok2/ngrok.ymlfile.