1) I don't think you can change the colour, but you can adjust the dimming level with:
defaults write com.googlecode.iterm2 SplitPaneDimmingAmount -float 0.25 # [range from 0-1.0, lower is darker]
Maybe add a feature request for a 'inactive panes colour' widget to be added to the Profile colours tab.
NB: Changing the dim amount seems to require a restart of iTerm to take effect.
2) Set a global keybinding (Prefs->Keys-> + button) to 'Select Menu Item...' from the very bottom of the list, and specify 'Next Pane' (no quotes) in the text field.
defaults write com.googlecode.iterm2 SplitPaneDimmingAmount -float 0.25 # [range from 0-1.0, lower is darker]
Maybe add a feature request for a 'inactive panes colour' widget to be added to the Profile colours tab.
NB: Changing the dim amount seems to require a restart of iTerm to take effect.
2) Set a global keybinding (Prefs->Keys-> + button) to 'Select Menu Item...' from the very bottom of the list, and specify 'Next Pane' (no quotes) in the text field.