Change background color in nix shell

home.nix

@@ -78,17 +78,24 @@ in rec {
     # We put PROMPT in initExtra instead of localVariables.PROMPT because nix puts the string in double quotes, whereas we want single quotes for the command to run each time
     initExtra =
       ''
+        get_stuff_in_nix() {
+          printf "%s" $PATH | tr ':' '\n' | grep '/nix/store' \
+            | sed -Ee 's|/nix/store/[0-9a-z]*-(.*)/.*|\1|g' \
+            | sed -Ee 's|-[0-9]+(\.[0-9]+)+||g' \
+            | tr '\n' ' '
+        }
         export PROMPT='$(
           BG=$PROMPT_COLOR
           FG=0
-          if [ ! -z $NIX_BUILD_CORES ] ; then
+          NIX_CONTENT="$(get_stuff_in_nix)"
-            BG=56
+          if [ ! -z "$NIX_BUILD_CORES" -o ! -z "$NIX_CONTENT" ] ; then
+            BG=91
             FG=15
           fi
           echo -en "%{\033[0m\033[38;5;''${FG}m\033[48;5;''${BG}m%} ";
           echo -n "["
           ${unambig-path}/bin/unambig-path
-          echo -en "] %T ";
+          echo -en "] $NIX_CONTENT%T ";
           echo -en "%{\033[0m\033[38:5:''${BG}m%}"
           echo -en "%{\033[0m%} ";
         )'