Why can't I get the cobalt2 zsh theme to work

I want to install this ZSH theme . I downloaded both the iTerm2 and ZSH themes.

The iTerm theme was imported through the preferences. The ZSH theme was inserted into ~/.oh-my-zsh/themes along with all the other ZSH themes.

When I open my .zshrc and change ZSH_THEME="bobbyrussell" to ZSH_THEME="cobalt2" nothing happens. I restart iTerm but the colors are not changed.

Updated with Details:

~ echo $ZSH_THEME
cobalt2

~ echo $PROMPT
%/ ~

File: ~/.zshrc

# Path to your oh-my-zsh installation.
export ZSH=/Users/username/.oh-my-zsh

# Set name of the theme to load.
# Look in ~/.oh-my-zsh/themes/
# Optionally, if you set this to "random", it'll load a random theme each
# time that oh-my-zsh is loaded.
ZSH_THEME="cobalt2"

# Uncomment the following line to use case-sensitive completion.
# CASE_SENSITIVE="true"

# Uncomment the following line to disable bi-weekly auto-update checks.
# DISABLE_AUTO_UPDATE="true"

# Uncomment the following line to change how often to auto-update (in days).
# export UPDATE_ZSH_DAYS=13

# Uncomment the following line to disable colors in ls.
# DISABLE_LS_COLORS="true"

# Uncomment the following line to disable auto-setting terminal title.
# DISABLE_AUTO_TITLE="true"

# Uncomment the following line to enable command auto-correction.
# ENABLE_CORRECTION="true"

# Uncomment the following line to display red dots whilst waiting for completion.
# COMPLETION_WAITING_DOTS="true"

# Uncomment the following line if you want to disable marking untracked files
# under VCS as dirty. This makes repository status check for large repositories
# much, much faster.
# DISABLE_UNTRACKED_FILES_DIRTY="true"

# Uncomment the following line if you want to change the command execution time
# stamp shown in the history command output.
# The optional three formats: "mm/dd/yyyy"|"dd.mm.yyyy"|"yyyy-mm-dd"
# HIST_STAMPS="mm/dd/yyyy"

# Would you like to use another custom folder than $ZSH/custom?
# ZSH_CUSTOM=/path/to/new-custom-folder

# Which plugins would you like to load? (plugins can be found in ~/.oh-my-zsh/plugins/*)
# Custom plugins may be added to ~/.oh-my-zsh/custom/plugins/
# Example format: plugins=(rails git textmate ruby lighthouse)
# Add wisely, as too many plugins slow down shell startup.
plugins=(git)

# User configuration

export PATH="/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/opt/X11/bin:/usr/local/git/bin"
# export MANPATH="/usr/local/man:$MANPATH"

source $ZSH/oh-my-zsh.sh

# You may need to manually set your language environment
# export LANG=en_US.UTF-8

# Preferred editor for local and remote sessions
# if [[ -n $SSH_CONNECTION ]]; then
#   export EDITOR='vim'
# else
#   export EDITOR='mvim'
# fi

# Compilation flags
# export ARCHFLAGS="-arch x86_64"

# ssh
# export SSH_KEY_PATH="~/.ssh/dsa_id"

# Set personal aliases, overriding those provided by oh-my-zsh libs,
# plugins, and themes. Aliases can be placed here, though oh-my-zsh
# users are encouraged to define aliases within the ZSH_CUSTOM folder.
# For a full list of active aliases, run `alias`.
#
# Example aliases
# alias zshconfig="mate ~/.zshrc"
# alias ohmyzsh="mate ~/.oh-my-zsh"

export PS1='%/ ~ '

The last line export PS1='%/ ~ ' of your .zshrc overwrites the prompt configured by cobalt2.zsh-theme, which sets $PROMPT (and the theme is sourced when you source $ZSH/oh-my-zsh.sh). As you can see, export PS1='%/ ~ ' comes after source $ZSH/oh-my-zsh.sh, so it overwrites the previous value. (Note that $PS1, $PROMPT and $prompt are synonyms to each other in Zsh.)

The solution is simple: delete the last line of your .zshrc and try again.