Add indicator for failed temperature fetching

src/c/settings.h

@@ -14,7 +14,7 @@ typedef struct ClaySettings {
   GColor ColorBarsHot;
   GColor ColorMGTime;
   GColor ColorFG;
-  GColor ColorLowFuel;
+  GColor ColorWarning;
 } __attribute__((__packed__)) ClaySettings;
 
 _Static_assert(sizeof(ClaySettings) <= 256, "ClaySettings exceeds Pebble 256-byte persist limit!");