diff --git a/lib/atlas/events/event_category.ex b/lib/atlas/events/event_category.ex
index 4bf3ea9..db381cf 100644
--- a/lib/atlas/events/event_category.ex
+++ b/lib/atlas/events/event_category.ex
@@ -25,6 +25,9 @@ defmodule Atlas.Events.EventCategory do
   def changeset(event_category, attrs) do
     event_category
     |> cast(attrs, @required_fields ++ @optional_fields)
+    |> validate_format(:color, ~r/^#[0-9a-fA-F]{6}$/,
+      message: "Invalid color format!(e.g., #RRGGBB)"
+    )
     |> validate_required(@required_fields)
   end
 end
diff --git a/test/atlas/events_test.exs b/test/atlas/events_test.exs
index 7551f9f..9ca5d60 100644
--- a/test/atlas/events_test.exs
+++ b/test/atlas/events_test.exs
@@ -21,11 +21,11 @@ defmodule Atlas.EventsTest do
     end
 
     test "create_event_category/1 with valid data creates a event_category" do
-      valid_attrs = %{name: "some name", color: "some color", type: "optional"}
+      valid_attrs = %{name: "some name", color: "#abcdef", type: "optional"}
 
       assert {:ok, %EventCategory{} = event_category} = Events.create_event_category(valid_attrs)
       assert event_category.name == "some name"
-      assert event_category.color == "some color"
+      assert event_category.color == "#abcdef"
     end
 
     test "create_event_category/1 with invalid data returns error changeset" do
@@ -34,13 +34,13 @@ defmodule Atlas.EventsTest do
 
     test "update_event_category/2 with valid data updates the event_category" do
       event_category = event_category_fixture()
-      update_attrs = %{name: "some updated name", color: "some updated color"}
+      update_attrs = %{name: "some updated name", color: "#123456"}
 
       assert {:ok, %EventCategory{} = event_category} =
                Events.update_event_category(event_category, update_attrs)
 
       assert event_category.name == "some updated name"
-      assert event_category.color == "some updated color"
+      assert event_category.color == "#123456"
     end
 
     test "update_event_category/2 with invalid data returns error changeset" do
diff --git a/test/atlas_web/controllers/event_category_controller_test.exs b/test/atlas_web/controllers/event_category_controller_test.exs
index 6a9edcf..6be0ae2 100644
--- a/test/atlas_web/controllers/event_category_controller_test.exs
+++ b/test/atlas_web/controllers/event_category_controller_test.exs
@@ -7,14 +7,14 @@ defmodule AtlasWeb.EventCategoryControllerTest do
 
   @create_attrs %{
     name: "some name",
-    color: "some color"
+    color: "#abcdef",
+    type: "optional"
   }
   @update_attrs %{
     name: "some updated name",
-    color: "some updated color"
+    color: "#123456",
+    type: "mandatory"
   }
-  @create_attrs Map.put(@create_attrs, :type, "optional")
-  @update_attrs Map.put(@update_attrs, :type, "optional")
   @invalid_attrs %{name: nil, color: nil, type: nil}
 
   setup %{conn: _conn} do
@@ -38,7 +38,7 @@ defmodule AtlasWeb.EventCategoryControllerTest do
 
       assert %{
                "id" => ^id,
-               "color" => "some color",
+               "color" => "#abcdef",
                "name" => "some name"
              } = json_response(conn, 200)["event_category"]
     end
@@ -63,7 +63,7 @@ defmodule AtlasWeb.EventCategoryControllerTest do
 
       assert %{
                "id" => ^id,
-               "color" => "some updated color",
+               "color" => "#123456",
                "name" => "some updated name"
              } = json_response(conn, 200)["event_category"]
     end
diff --git a/test/support/fixtures/events_fixtures.ex b/test/support/fixtures/events_fixtures.ex
index ff734dc..0a1f2ea 100644
--- a/test/support/fixtures/events_fixtures.ex
+++ b/test/support/fixtures/events_fixtures.ex
@@ -11,8 +11,8 @@ defmodule Atlas.EventsFixtures do
     {:ok, event_category} =
       attrs
       |> Enum.into(%{
-        color: "some color",
         name: "some name",
+        color: "#abcdef",
         type: "optional"
       })
       |> Atlas.Events.create_event_category()
@@ -26,18 +26,16 @@ defmodule Atlas.EventsFixtures do
   def event_fixture(attrs \\ %{}) do
     category = event_category_fixture()
 
-    defaults = %{
-      end: ~N[2025-01-01 14:00:00],
-      link: "some link",
-      place: "some place",
-      start: ~N[2025-01-01 14:00:00],
-      title: "some title",
-      category_id: category.id
-    }
-
     {:ok, event} =
       attrs
-      |> Enum.into(defaults)
+      |> Enum.into(%{
+        title: "some title",
+        start: ~U[2025-01-01T14:00:00Z],
+        end: ~U[2025-01-01T15:00:00Z],
+        place: "some place",
+        link: "some link",
+        category_id: category.id
+      })
       |> Atlas.Events.create_event()
 
     event