How do you change colour scheme between *panes* inside iTerm2 + oh-my-zsh?
The easiest way of doing this is to install the "Shell Integration" tools, using this menu in iTerm:



Once you've done that you will have access to several iTerm-specific tools, including it2setcolor which lets you easily change the colors.

For example, I use this as part of my ssh alias for connecting to a remote server:

it2setcolor preset 'Solarized Light'


so whenever I ssh somewhere, iTerm automatically changes the 'Theme' to 'Solarized Light'.

(Run it2setcolor with no args to get a usage summary.)