diff --git a/app/models/category.rb b/app/models/category.rb
index 94d5097e1..39a740f7d 100644
--- a/app/models/category.rb
+++ b/app/models/category.rb
@@ -9,6 +9,7 @@ class Category < ApplicationRecord
   belongs_to :parent, class_name: "Category", optional: true
 
   validates :name, :color, :lucide_icon, :family, presence: true
+  validates :color, format: { with: /\A#[0-9A-Fa-f]{6}\z/ }
   validates :name, uniqueness: { scope: :family_id }
 
   validate :category_level_limit
diff --git a/app/views/categories/_form.html.erb b/app/views/categories/_form.html.erb
index 3b9e6f1b4..1f3e5fbeb 100644
--- a/app/views/categories/_form.html.erb
+++ b/app/views/categories/_form.html.erb
@@ -30,7 +30,7 @@
               <div class="flex gap-2 items-center hidden flex-col" data-category-target="paletteSection">
                 <div class="flex gap-2 items-center w-full">
                   <div class="w-6 h-6 p-4 rounded-full cursor-pointer" style="background-color: <%= category.color %>" data-category-target="colorPreview"></div>
-                  <%= f.text_field :color , data: { category_target: "colorInput"}, inline: true %>
+                  <%= f.text_field :color, data: { category_target: "colorInput" }, inline: true, pattern: "^#[0-9A-Fa-f]{6}$" %>
                   <%= icon "palette", size: "2xl", data: { action: "click->category#toggleSections" } %>
                 </div>
                 <div data-category-target="validationMessage" class="hidden self-start flex gap-1 items-center text-xs text-destructive ">
diff --git a/test/models/budget_test.rb b/test/models/budget_test.rb
index f681bebc2..13f8f5a2b 100644
--- a/test/models/budget_test.rb
+++ b/test/models/budget_test.rb
@@ -264,7 +264,7 @@ class BudgetTest < ActiveSupport::TestCase
     source_budget.update!(budgeted_spending: 4000, expected_income: 6000)
 
     # Create a category only in the source budget
-    temp_category = Category.create!(name: "Temp #{Time.now.to_f}", family: family, color: "#aaa")
+    temp_category = Category.create!(name: "Temp #{Time.now.to_f}", family: family, color: "#aaaaaa")
     source_budget.budget_categories.create!(category: temp_category, budgeted_spending: 100, currency: "USD")
 
     target_budget = Budget.find_or_bootstrap(family, start_date: 1.month.ago)
@@ -283,7 +283,7 @@ class BudgetTest < ActiveSupport::TestCase
     target_budget = Budget.find_or_bootstrap(family, start_date: 1.month.ago)
 
     # Add a new category only to the target
-    new_category = Category.create!(name: "New #{Time.now.to_f}", family: family, color: "#bbb")
+    new_category = Category.create!(name: "New #{Time.now.to_f}", family: family, color: "#bbbbbb")
     target_budget.budget_categories.create!(category: new_category, budgeted_spending: 0, currency: "USD")
 
     target_budget.copy_from!(source_budget)
diff --git a/test/models/category_test.rb b/test/models/category_test.rb
index da4f9a48a..fc4036600 100644
--- a/test/models/category_test.rb
+++ b/test/models/category_test.rb
@@ -40,4 +40,19 @@ class CategoryTest < ActiveSupport::TestCase
     assert names.all? { |name| name.is_a?(String) }
     assert_equal names, names.uniq  # No duplicates
   end
+
+  test "should accept valid 6-digit hex colors" do
+    [ "#FFFFFF", "#000000", "#123456", "#ABCDEF", "#abcdef" ].each do |color|
+      category = Category.new(name: "Category #{color}", color: color, lucide_icon: "shapes", family: @family)
+      assert category.valid?, "#{color} should be valid"
+    end
+  end
+
+  test "should reject invalid colors" do
+    [ "invalid", "#123", "#1234567", "#GGGGGG", "red", "ffffff", "#ffff", "" ].each do |color|
+      category = Category.new(name: "Category #{color}", color: color, lucide_icon: "shapes", family: @family)
+      assert_not category.valid?, "#{color} should be invalid"
+      assert_includes category.errors[:color], "is invalid"
+    end
+  end
 end