diff --git a/server/src/wled_controller/static/css/base.css b/server/src/wled_controller/static/css/base.css
index 8266f51..88ee926 100644
--- a/server/src/wled_controller/static/css/base.css
+++ b/server/src/wled_controller/static/css/base.css
@@ -102,6 +102,35 @@ body.modal-open {
     background: transparent;
 }
 
+/* ── Tab indicator (background watermark) ── */
+#tab-indicator {
+    position: fixed;
+    right: -10vw;
+    top: 50%;
+    transform: translateY(-50%);
+    width: 55vw;
+    height: 55vw;
+    max-width: 600px;
+    max-height: 600px;
+    pointer-events: none;
+    z-index: -1;
+    opacity: 0;
+    filter: blur(6px);
+    color: var(--primary-color);
+    transition: opacity 0.5s ease;
+}
+#tab-indicator svg {
+    width: 100%;
+    height: 100%;
+    opacity: 0.04;
+}
+#tab-indicator.tab-indicator-visible {
+    opacity: 1;
+}
+[data-theme="light"] #tab-indicator svg {
+    opacity: 0.035;
+}
+
 .container {
     padding: 20px;
 }
diff --git a/server/src/wled_controller/static/js/app.js b/server/src/wled_controller/static/js/app.js
index 425a837..05cad71 100644
--- a/server/src/wled_controller/static/js/app.js
+++ b/server/src/wled_controller/static/js/app.js
@@ -13,6 +13,7 @@ import { t, initLocale, changeLocale } from './core/i18n.js';
 // Layer 1.5: visual effects
 import { initCardGlare } from './core/card-glare.js';
 import { initBgAnim, updateBgAnimAccent, updateBgAnimTheme } from './core/bg-anim.js';
+import { initTabIndicator, updateTabIndicator } from './core/tab-indicator.js';
 
 // Layer 2: ui
 import {
@@ -173,6 +174,7 @@ Object.assign(window, {
     // visual effects (called from inline <script>)
     _updateBgAnimAccent: updateBgAnimAccent,
     _updateBgAnimTheme: updateBgAnimTheme,
+    _updateTabIndicator: updateTabIndicator,
 
     // core / ui
     toggleHint,
@@ -539,6 +541,7 @@ document.addEventListener('DOMContentLoaded', async () => {
     // Initialize visual effects
     initCardGlare();
     initBgAnim();
+    initTabIndicator();
     updateBgAnimTheme(document.documentElement.getAttribute('data-theme') !== 'light');
     const accent = localStorage.getItem('accentColor') || '#4CAF50';
     updateBgAnimAccent(accent);
diff --git a/server/src/wled_controller/static/js/core/tab-indicator.js b/server/src/wled_controller/static/js/core/tab-indicator.js
new file mode 100644
index 0000000..bd14100
--- /dev/null
+++ b/server/src/wled_controller/static/js/core/tab-indicator.js
@@ -0,0 +1,47 @@
+/**
+ * Tab indicator — large semi-transparent blurred icon on the right side
+ * of the viewport, reflecting the currently active tab.
+ */
+
+const TAB_SVGS = {
+    dashboard: `<svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.2" stroke-linecap="round" stroke-linejoin="round"><rect width="7" height="9" x="3" y="3" rx="1"/><rect width="7" height="5" x="14" y="3" rx="1"/><rect width="7" height="9" x="14" y="12" rx="1"/><rect width="7" height="5" x="3" y="16" rx="1"/></svg>`,
+    automations: `<svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.2" stroke-linecap="round" stroke-linejoin="round"><rect width="8" height="4" x="8" y="2" rx="1" ry="1"/><path d="M16 4h2a2 2 0 0 1 2 2v14a2 2 0 0 1-2 2H6a2 2 0 0 1-2-2V6a2 2 0 0 1 2-2h2"/><path d="M12 11h4"/><path d="M12 16h4"/><path d="M8 11h.01"/><path d="M8 16h.01"/></svg>`,
+    targets: `<svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.2" stroke-linecap="round" stroke-linejoin="round"><path d="M4 14a1 1 0 0 1-.78-1.63l9.9-10.2a.5.5 0 0 1 .86.46l-1.92 6.02A1 1 0 0 0 13 10h7a1 1 0 0 1 .78 1.63l-9.9 10.2a.5.5 0 0 1-.86-.46l1.92-6.02A1 1 0 0 0 11 14z"/></svg>`,
+    streams: `<svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.2" stroke-linecap="round" stroke-linejoin="round"><path d="m17 2-5 5-5-5"/><rect width="20" height="15" x="2" y="7" rx="2"/></svg>`,
+};
+
+let _el = null;
+let _currentTab = null;
+
+function _ensureEl() {
+    if (_el) return _el;
+    _el = document.createElement('div');
+    _el.id = 'tab-indicator';
+    _el.setAttribute('aria-hidden', 'true');
+    document.body.appendChild(_el);
+    return _el;
+}
+
+export function updateTabIndicator(tabName) {
+    if (tabName === _currentTab) return;
+    _currentTab = tabName;
+    const svg = TAB_SVGS[tabName];
+    if (!svg) return;
+
+    const el = _ensureEl();
+    // Trigger crossfade: set opacity 0, swap content, fade in
+    el.classList.remove('tab-indicator-visible');
+    setTimeout(() => {
+        el.innerHTML = svg;
+        el.classList.add('tab-indicator-visible');
+    }, 200);
+}
+
+export function initTabIndicator() {
+    _ensureEl();
+    // Set initial tab from current active button
+    const active = document.querySelector('.tab-btn.active');
+    if (active) {
+        updateTabIndicator(active.dataset.tab);
+    }
+}
diff --git a/server/src/wled_controller/static/js/features/tabs.js b/server/src/wled_controller/static/js/features/tabs.js
index 17c8f4c..71c8d54 100644
--- a/server/src/wled_controller/static/js/features/tabs.js
+++ b/server/src/wled_controller/static/js/features/tabs.js
@@ -37,6 +37,9 @@ export function switchTab(name, { updateHash = true, skipLoad = false } = {}) {
     document.querySelectorAll('.tab-panel').forEach(panel => panel.classList.toggle('active', panel.id === `tab-${name}`));
     localStorage.setItem('activeTab', name);
 
+    // Update background tab indicator
+    if (typeof window._updateTabIndicator === 'function') window._updateTabIndicator(name);
+
     // Restore scroll position for this tab
     requestAnimationFrame(() => window.scrollTo(0, _tabScrollPositions[name] || 0));