nexrad default palette to rgba

crates/tiler/src/nexrad.rs

@@ -342,11 +342,7 @@ fn colorize(
                 color.red,
                 color.green,
                 color.blue,
-                if color.red == 0 && color.green == 0 && color.blue == 0 {
+                color.alpha,
-                    0
-                } else {
-                    255
-                },
             ])
         }
         None => Rgba([0, 0, 0, 30]),