Add method to get defult leather color. Adds BUKKIT-3203

The default leather color is already used internally in place of null. The
javadocs were updated appropriately to indicate as such.

By: Wesley Wolfe <weswolf@aol.com>

paper-api/src/main/java/org/bukkit/inventory/ItemFactory.java

@@ -1,5 +1,6 @@
 package org.bukkit.inventory;
 
+import org.bukkit.Color;
 import org.bukkit.Material;
 import org.bukkit.Server;
 import org.bukkit.inventory.meta.BookMeta;
@@ -79,4 +80,11 @@ public interface ItemFactory {
      * @throws IllegalArgumentException if the specified meta was not created by this factory
      */
     ItemMeta asMetaFor(final ItemMeta meta, final Material material) throws IllegalArgumentException;
+
+    /**
+     * Returns the default color for all leather armor.
+     *
+     * @return the default color for leather armor
+     */
+    Color getDefaultLeatherColor();
 }

paper-api/src/main/java/org/bukkit/inventory/meta/LeatherArmorMeta.java

@@ -2,6 +2,7 @@ package org.bukkit.inventory.meta;
 
 import org.bukkit.Color;
 import org.bukkit.Material;
+import org.bukkit.inventory.ItemFactory;
 
 /**
  * Represents leather armor ({@link Material#LEATHER_BOOTS}, {@link Material#LEATHER_CHESTPLATE}, {@link Material#LEATHER_HELMET}, or {@link Material#LEATHER_LEGGINGS}) that can be colored.
@@ -9,16 +10,16 @@ import org.bukkit.Material;
 public interface LeatherArmorMeta extends ItemMeta {
 
     /**
-     * Gets the color of the armor
+     * Gets the color of the armor. If it has not been set otherwise, it will be {@link ItemFactory#getDefaultLeatherColor()}.
      *
      * @return the color of the armor, never null
      */
     Color getColor();
 
     /**
-     * Sets the color of the armor
+     * Sets the color of the armor.
      *
-     * @param color the color to set, null makes it the default leather color
+     * @param color the color to set. Setting it to null is equivalent to setting it to {@link ItemFactory#getDefaultLeatherColor()}.
      */
     void setColor(Color color);