Add EntityDyeEvent and CollarColorable interface

paper-api/src/main/java/io/papermc/paper/entity/CollarColorable.java

@@ -0,0 +1,26 @@
+package io.papermc.paper.entity;
+
+import org.bukkit.DyeColor;
+import org.bukkit.entity.LivingEntity;
+import org.jspecify.annotations.NullMarked;
+
+/**
+ * Entities that can have their collars colored.
+ */
+@NullMarked
+public interface CollarColorable extends LivingEntity {
+
+    /**
+     * Get the collar color of this entity
+     *
+     * @return the color of the collar
+     */
+    DyeColor getCollarColor();
+
+    /**
+     * Set the collar color of this entity
+     *
+     * @param color the color to apply
+     */
+    void setCollarColor(DyeColor color);
+}