Change WezTerm background color based on SSH host; copy this snippet to your WezTerm config + define your own host_to_color mapping

snippet-wezterm.lua

-- Hash char is here to make good editors show the color in situ.
local host_to_color = {
  ["main.*p"] = "#660000",
  ["other.*q"] = "#660066",
  -- key = a pattern to match a hostname
  -- value = the color to use as pane background for the hostname
}
local colored_panes = {}
wezterm.on("update-status", function(window, pane)
  local fg = pane:get_foreground_process_info() or {}
  if fg.name == "ssh" then
    for ndx = 2, #fg.argv do
      for k, v in pairs(host_to_color) do
        if string.find(fg.argv[ndx], k) then
          if not colored_panes[pane:pane_id()] then
            -- print(">>> NEW")
            pane:inject_output(string.format("\x1b]11;%s\x07", string.sub(v, 2)))
            colored_panes[pane:pane_id()] = fg.pid
          end
        end
      end
    end
  else
    if colored_panes[pane:pane_id()] then
      local ssh = wezterm.procinfo.get_info_for_pid(colored_panes[pane:pane_id()])
        if not ssh then
          -- print(">>> CLEARED")
          colored_panes[pane:pane_id()] = nil
          pane:inject_output("\x1b]104\x07")
        end
    end
  end
end)