prompt bug fix

profile.sh

@@ -278,10 +278,22 @@ parse_conf()
             value="${value//\`/}"
             value="${value//\$\(/}"
 
-            # Correctly interpretet internal variables (e.g. $HOME)
+            # Correctly interpretet internal variables (e.g. $HOME). In the
+            # [prompt] section only the variables that exist are substituted:
+            # envsubst would otherwise replace an unknown one by nothing,
+            # wiping out the $Blue-style colour references that are resolved
+            # later, when the colour variables exist (see prompt.sh).
             if [[ "$value" == *\$* ]]; then
                 if command -v envsubst >/dev/null 2>&1; then
-                    value=$(envsubst <<< "$value")
+                    if [[ "$current_section" == "prompt" ]]; then
+                        local _envnames="" _envname
+                        for _envname in $(compgen -e); do
+                            [[ "$_envname" =~ ^[A-Za-z_][A-Za-z0-9_]*$ ]] && _envnames+="\${${_envname}}"
+                        done
+                        value=$(envsubst "$_envnames" <<< "$value")
+                    else
+                        value=$(envsubst <<< "$value")
+                    fi
                 fi
                 # If envsubst is unavailable, $VAR references are left as-is.
             fi