change how script colour is handled

langfilter/main/Main.hs

@@ -1,4 +1,17 @@
+import qualified Data.Map as Map
+import qualified Data.Text as Text
 import LangFilter
+import System.Environment
 import Text.Pandoc.JSON
+import Lang
 
-main = toJSONFilter langFilter
+main =
+  toJSONFilter $ \p@(Pandoc (Meta m) _) -> do
+    col <- getDefColor m
+    langFilter col p
+ where
+  getDefColor m = do
+    res <- toText $ Map.lookup "lang-color" m
+    case res of
+      Just col -> pure $ col
+      Nothing  -> maybe "currentcolor" Text.pack <$> lookupEnv "LANG_COLOR"