properly handle dimming tint color (white color space, not RGB)

@@ -118,10 +118,16 @@
     
     if (color)
     {
-        CGFloat red, green, blue, alpha;
+        CGFloat white, red, green, blue, alpha;
 
         if ([color getRed:&red green:&green blue:&blue alpha:&alpha])
+        {
             colorHex = [NSString stringWithFormat:@"%02x%02x%02x", (NSUInteger)(red * 255), (NSUInteger)(green * 255), (NSUInteger)(blue * 255)];
+        }
+        else if ([color getWhite:&white alpha:&alpha])
+        {
+            colorHex = [NSString stringWithFormat:@"%02x%02x%02x", (NSUInteger)(white * 255), (NSUInteger)(white * 255), (NSUInteger)(white * 255)];
+        }
     }
     
     return [self initWithMapBoxMarkerImage:symbolName tintColorHex:colorHex sizeString:sizeString];