Add Color record struct, small refactor, create a DaggerFramework.SceneGraph namespace.

Source/SceneGraph/EntityLayer.cs

@@ -0,0 +1,58 @@
+using DaggerFramework.Rendering;
+
+namespace DaggerFramework.SceneGraph
+{
+    public class EntityLayer : Layer
+    {
+        public List<Entity> Entities { get => _entities; }
+        public EntityLayer(List<Entity> entities)
+        {
+            _entities = entities;
+        }
+
+        public EntityLayer()
+        {
+            _entities = new List<Entity>();
+        }
+
+        public bool AddEntity(Entity entity)
+        {
+            entity.Id = Entities.Count;
+            entity.Layer = this;
+            Entities.Add(entity);
+            return true;
+        }
+
+        public void DestroyEntity(int at)
+        {
+            _entities.RemoveAt(at);
+        }
+
+        protected override void OnStart()
+        {
+            foreach (var entity in _entities)
+            {
+                entity.Layer = this;
+                entity.Start();
+            }
+        }
+
+        protected override void OnUpdate(double dt)
+        {
+            foreach (var entity in _entities)
+            {
+                entity.Update(dt);
+            }
+        }
+
+        protected override void OnDraw(Renderer renderer)
+        {
+            foreach (IDrawable drawable in _entities)
+            {
+                drawable.Draw(renderer);
+            }
+        }
+
+        private List<Entity> _entities;
+    }
+}