Replace $BASH with $BASH_IT because $BASH is already used on *nix systems for the pathname to the executable (http://www.gnu.org/software/bash/manual/html_node/Bash-Variables.html#Bash-Variables)

lib/appearance.bash

@@ -8,6 +8,6 @@ export GREP_COLOR='1;33'
 export LSCOLORS='Gxfxcxdxdxegedabagacad'
 
 # Load the theme
-if [[ $BASH_THEME ]]; then
-    source "$BASH/themes/$BASH_THEME/$BASH_THEME.theme.bash"
-fi
+if [[ $BASH_IT_THEME ]]; then
+    source "$BASH_IT/themes/$BASH_IT_THEME/$BASH_IT_THEME.theme.bash"
+fi