Make ForgeSpawnEgg assume color is opaque if alpha is set to 0.

Fixes "invisible" spawn eggs by default, but still allows modders to specify partial transparency.

src/main/java/net/minecraftforge/common/ForgeSpawnEggItem.java

@@ -7,6 +7,7 @@ package net.minecraftforge.common;
 
 import net.minecraft.core.Direction;
 import net.minecraft.core.dispenser.DispenseItemBehavior;
+import net.minecraft.util.FastColor;
 import net.minecraft.world.entity.EntityType;
 import net.minecraft.world.entity.Mob;
 import net.minecraft.world.entity.MobSpawnType;
@@ -91,9 +92,14 @@ public class ForgeSpawnEggItem extends SpawnEggItem {
     private static class ColorRegisterHandler {
         @SubscribeEvent(priority = EventPriority.HIGHEST)
         public static void registerSpawnEggColors(RegisterColorHandlersEvent.Item event) {
-            MOD_EGGS.forEach(egg ->
-                event.register((stack, layer) -> egg.getColor(layer), egg)
-            );
+            MOD_EGGS.forEach(egg -> {
+                event.register((stack, layer) -> {
+                    int color = egg.getColor(layer);
+                    if (FastColor.ARGB32.alpha(color) == 0)
+                        color = FastColor.ARGB32.opaque(color);
+                    return color;
+                }, egg);
+            });
         }
     }
 }