diff --git a/frontend/index.html b/frontend/index.html
index 08d43c5..e11aef1 100644
--- a/frontend/index.html
+++ b/frontend/index.html
@@ -16296,7 +16296,17 @@ function pysimFsFilterRender() {
 		}
 		menu.innerHTML = out;
 	}
-	if (btn) btn.textContent = pysimFsFilterSummary();
+	if (btn) {
+		btn.textContent = pysimFsFilterSummary();
+		// a non-"All" selection stands out (blue, like the active sort pill)
+		const active = pysimFsFilter.size > 0 && !pysimFsFilter.has(FS_FILTER_ALL);
+		btn.classList.toggle('bg-blue-600', active);
+		btn.classList.toggle('text-white', active);
+		btn.classList.toggle('text-gray-700', !active);
+		btn.classList.toggle('dark:text-slate-300', !active);
+		btn.classList.toggle('hover:bg-gray-200', !active);
+		btn.classList.toggle('dark:hover:bg-slate-700', !active);
+	}
 }
 
 // Expand or collapse the menu (`force` overrides the toggle; the outside
diff --git a/frontend/tests/fs_filter.test.js b/frontend/tests/fs_filter.test.js
index b2c0928..2a447f5 100644
--- a/frontend/tests/fs_filter.test.js
+++ b/frontend/tests/fs_filter.test.js
@@ -73,9 +73,19 @@ globalThis.pysimFsRenderTree = () => { _treeRenders++; };
 // menu it expands into.  The menu only needs a settable innerHTML (the
 // render never reads the DOM back) and a classList for the open/closed state.
 function fakeBtn() {
+	const classes = new Set();
 	return {
 		textContent: '',
 		attrs: {},
+		classes,
+		classList: {
+			contains: c => classes.has(c),
+			toggle(c, force) {
+				const on = force === undefined ? !classes.has(c) : !!force;
+				if (on) classes.add(c); else classes.delete(c);
+				return on;
+			},
+		},
 		setAttribute(k, v) { this.attrs[k] = String(v); },
 		getAttribute(k) { return this.attrs[k]; },
 	};
@@ -429,6 +439,21 @@ test('the menu lists all, custom, the three headings and the services', () => {
 	assert.match(out, /onchange="pysimFsFilterSetEntry\(this\.dataset\.filter, this\.checked\)"/);
 });
 
+test('the button turns blue when a filter is active and back for all', () => {
+	dom.menu = fakeMenu();
+	dom.btn = fakeBtn();
+	pysimFsFilter = new Set(['identifiers']);
+	pysimFsFilterRender();
+	assert.strictEqual(dom.btn.classes.has('bg-blue-600'), true);
+	assert.strictEqual(dom.btn.classes.has('text-white'), true);
+	assert.strictEqual(dom.btn.classes.has('text-gray-700'), false);
+	pysimFsFilter = new Set(['all']);
+	pysimFsFilterRender();
+	assert.strictEqual(dom.btn.classes.has('bg-blue-600'), false);
+	assert.strictEqual(dom.btn.classes.has('text-white'), false);
+	assert.strictEqual(dom.btn.classes.has('text-gray-700'), true);
+});
+
 test('the menu marks the saved selection', () => {
 	pysimFsFilter = new Set(['svc:Short Message Storage (SMS)', 'identifiers']);
 	dom.menu = fakeMenu();