Give a more useful error if the biome color png files can't be found

chunk.py

@@ -170,6 +170,12 @@ class ChunkRenderer(object):
         _, dir1 = os.path.split(moredirs)
         self.cachedir = os.path.join(cachedir, dir1, dir2)
 
+
+        if self.world.useBiomeData:
+            if not textures.grasscolor or not textures.foliagecolor:
+                raise Exception("Can't find grasscolor.png or foliagecolor.png")
+
+
         if not os.path.exists(self.cachedir):
             try:
                 os.makedirs(self.cachedir)

textures.py

@@ -564,7 +564,8 @@ try:
     grasscolor = list(Image.open(_find_file("grasscolor.png")).getdata())
     foliagecolor = list(Image.open(_find_file("foliagecolor.png")).getdata())
 except:
-    pass
+    grasscolor = None
+    foliagecolor = None
 
 currentBiomeFile = None
 currentBiomeData = None