Built with IRC use in mind, both Light and Dark variants.
mkdir -p "$HOME/Library/Application Support/Adium 2.0/Message Styles/Solarized.AdiumMessageStyle" && git clone git@github.com:bs-github/Adium-Solarized.git "$HOME/Library/Application Support/Adium 2.0/Message Styles/Solarized.AdiumMessageStyle"
Then switch to the Message Style in the Messages section of the Adium preferences.