diff --git a/frontend/index.html b/frontend/index.html
index 677b96c..17b7f78 100644
--- a/frontend/index.html
+++ b/frontend/index.html
@@ -111,6 +111,10 @@ body { font: 14px/1.5 system-ui, sans-serif; background: var(--bg); color: var(-
 .apdu-type.pps { color: var(--yellow); }
 .apdu-data { font-family: monospace; color: var(--text-dim); word-break: break-all; flex: 1; }
 .apdu-sw { font-family: monospace; color: var(--text-muted); white-space: nowrap; min-width: 52px; }
+.apdu-sw.sw-ok { color: var(--green); }
+.apdu-sw.sw-pending { color: var(--accent); }
+.apdu-sw.sw-warn { color: var(--warn); }
+.apdu-sw.sw-error { color: var(--error); }
 
 /* APDU detail panel */
 .apdu-detail { display: flex; flex-direction: column; max-height: 40%; overflow-y: auto; border-top: 2px solid var(--accent); background: var(--bg-panel); flex-shrink: 0; }
@@ -453,6 +457,17 @@ function sw_text(m) {
     return d.sw.sw1 + ' ' + d.sw.sw2;
 }
 
+function sw_class(m) {
+    const d = m.decoded;
+    if (!d || !d.sw) return '';
+    const s = d.sw.sw1;
+    if (s === '90' || (s >= '92' && s <= '9f')) return 'sw-ok';
+    if (s === '61' || s === '91' || s === '6c') return 'sw-pending';
+    if (s === '62' || s === '63') return 'sw-warn';
+    if (s >= '64' && s <= '6f') return 'sw-error';
+    return '';
+}
+
 // ──────────────────── API ────────────────────
 const API = {
     async _fetch(method, path, body) {
@@ -974,7 +989,7 @@ function renderMessages() {
         return `<div class="apdu-entry" data-idx="${idx}">
             <span class="apdu-time">${fmt_elapsed(m.elapsed)}</span>
             <span class="apdu-type ${typeCls}">${label}</span>
-            <span class="apdu-sw">${sw_text(m)}</span>
+            <span class="apdu-sw ${sw_class(m)}">${sw_text(m)}</span>
             <span class="apdu-data">${cmd_description(m)}</span>
         </div>`;
     }).join('');
diff --git a/simtrace2_pysniff/server/decode.py b/simtrace2_pysniff/server/decode.py
index f22f10b..deed7c9 100644
--- a/simtrace2_pysniff/server/decode.py
+++ b/simtrace2_pysniff/server/decode.py
@@ -2213,6 +2213,8 @@ def _decode_phase(raw, p1=None):
 
 def _decode_nai(raw, p1=None):
     """ISIM identity files (EF_IMPI/DOMAIN/IMPU): BER-TLV tag 0x80 + ASCII value."""
+    if not raw or all(b == 0xff for b in raw):
+        return {'empty': True}
     texts = []
     for tag, _length, value in parse_tlv(raw):
         if tag == 0x80:
@@ -2221,7 +2223,7 @@ def _decode_nai(raw, p1=None):
                 texts.append(txt)
     if texts:
         return {'text': texts[0] if len(texts) == 1 else ', '.join(texts)}
-    txt = raw.decode('ascii', 'replace').replace('\xff', '').strip()
+    txt = raw.rstrip(b'\xff').decode('ascii', 'replace').strip()
     return {'text': txt} if txt else {'raw': raw.hex().upper()}
 
 
diff --git a/tests/test_decode.py b/tests/test_decode.py
index 8c2e5ed..569deb0 100644
--- a/tests/test_decode.py
+++ b/tests/test_decode.py
@@ -901,6 +901,20 @@ class TestFileDecoders(unittest.TestCase):
         self.assertEqual(f['applications'][0]['label'], 'MegaFon')
         self.assertEqual(f['applications'][0]['aid'], 'A0000000871002FFFFF00189000001FF')
 
+    def test_nai_empty_record(self):
+        from simtrace2_pysniff.server.decode import _decode_file_data
+        # Unused ISIM record (all FF) must be 'empty', not garbage text.
+        f = _decode_file_data('6f04', b'\xff' * 75)
+        self.assertTrue(f['empty'])
+        self.assertNotIn('text', f)
+
+    def test_nai(self):
+        from simtrace2_pysniff.server.decode import _decode_file_data
+        f = _decode_file_data('6f04', bytes.fromhex(
+            '80357369703a32353030323639333537373333363840696d732e6d6e63'
+            '3030322e6d63633235302e336770706e6574776f726b2e6f7267'))
+        self.assertEqual(f['text'], 'sip:250026935773368@ims.mnc002.mcc250.3gppnetwork.org')
+
     def test_plmn_wact(self):
         from simtrace2_pysniff.server.decode import _decode_file_data
         # TS 51.011 §10.3.35: 5-byte entries (3 PLMN + 2 access tech).