diff --git a/index.html b/index.html
index 89f4a17..d5992b2 100644
--- a/index.html
+++ b/index.html
@@ -278,6 +278,24 @@
   .veh-marker.has-type.parked .veh-pin { transform: scale(1); border-radius: 50%; }
   .veh-marker.has-type.offline .veh-type svg { opacity: .85; }
 
+  /* ── Cost-centre colour key (collapsible, tidy) ────────────────────── */
+  #legend { position: absolute; left: 10px; bottom: 12px; z-index: 5;
+    font: 600 11px system-ui; color: #fff; user-select: none; }
+  .legend-toggle { cursor: pointer; border: 1px solid var(--border);
+    background: rgba(15,18,23,.92); color: #fff; font: 600 11px system-ui;
+    padding: 4px 10px; border-radius: 6px; box-shadow: 0 2px 8px rgba(0,0,0,.45); }
+  .legend-toggle::before { content: '◑'; color: var(--accent); margin-right: 5px; }
+  .legend-body { margin-top: 6px; background: rgba(15,18,23,.92);
+    border: 1px solid var(--border); border-radius: 8px; padding: 7px 9px;
+    box-shadow: 0 4px 14px rgba(0,0,0,.5); max-height: 38vh; overflow-y: auto;
+    display: grid; gap: 4px; min-width: 124px; }
+  #legend.collapsed .legend-body { display: none; }
+  .legend-row { display: flex; align-items: center; gap: 7px; }
+  .legend-dot { width: 11px; height: 11px; border-radius: 3px; flex: 0 0 auto;
+    border: 1px solid rgba(255,255,255,.5); }
+  .legend-lbl { flex: 1; text-transform: uppercase; letter-spacing: .02em; }
+  .legend-n { color: var(--muted); font-weight: 700; }
+
   /* ── Persistent POI marker (Fireside HQ) ───────────────────────────── */
   /* Cluster bubble (zoomed-out): amber circle + white count, tiered by size.
      Click zooms to expand into the individual pins. */
@@ -379,6 +397,13 @@
 
   <div id="map">
     <div class="placeholder" id="placeholder">Loading live fleet…</div>
+    <!-- Cost-centre colour key — collapsed by default to keep the map tidy.
+         Lists only centres currently on screen; safe to delete this block + its
+         CSS/JS (renderLegend) to remove the feature entirely. -->
+    <div id="legend" class="collapsed" aria-label="Cost-centre colour key">
+      <button type="button" class="legend-toggle" id="legend-toggle">Key</button>
+      <div class="legend-body" id="legend-body"></div>
+    </div>
   </div>
 
   <!-- Bottom dock: two tiers — filter tier (top) + trip-card tier (beneath) -->
@@ -455,10 +480,26 @@ const STALE_GPS_MS = 10 * 60 * 1000;
 const OFFLINE_THRESHOLD_MS = 24 * 60 * 60 * 1000;
 const POIS = [{ name: 'Fireside HQ', lng: 36.728785, lat: -1.2411485 }];
 
-// Cost-centre palette — categorical, brand colours lead. Stable per centre via hash.
+// Deliberate, distinct colour per cost centre so all vehicles in a centre share
+// one colour and different centres are easy to tell apart at a glance. Keys are
+// normalised (lowercase, trimmed). Anything not listed falls back to a stable
+// hash of COST_CENTRE_PALETTE.
+const COST_CENTRE_COLORS = {
+  'isp':        '#3b82f6',  // blue
+  'osp':        '#E8954A',  // brand amber
+  'osp patrol': '#f97316',  // orange (OSP sibling)
+  'fds':        '#22c55e',  // green
+  'roll out':   '#a855f7',  // purple
+  'general':    '#fbbf24',  // gold
+  'regional':   '#ec4899',  // pink
+  'planning':   '#06b6d4',  // cyan
+  'deliveries': '#84cc16',  // lime
+  'qehs':       '#14b8a6',  // teal
+  'airtel':     '#ef4444',  // brand red
+};
+// Fallback palette for any centre not in COST_CENTRE_COLORS (stable per name via hash).
 const COST_CENTRE_PALETTE = [
-  '#E8954A', '#2dd4a7', '#3b82f6', '#a855f7', '#f43f5e', '#06b6d4',
-  '#84cc16', '#ec4899', '#fbbf24', '#14b8a6', '#8b5cf6', '#f97316', '#22c55e',
+  '#2dd4a7', '#8b5cf6', '#f43f5e', '#0ea5e9', '#eab308', '#d946ef', '#10b981',
 ];
 const UNKNOWN_CC_COLOR = '#9ca3af';
 const PARKED_COLOR = '#6b7280';
@@ -472,8 +513,10 @@ const seqColor = n => SEQ_PALETTE[((n || 1) - 1 + SEQ_PALETTE.length * 100) % SE
 
 function colorForCostCentre(cc) {
   if (!cc) return UNKNOWN_CC_COLOR;
+  const key = String(cc).trim().toLowerCase();
+  if (COST_CENTRE_COLORS[key]) return COST_CENTRE_COLORS[key];
   let h = 0;
-  for (let i = 0; i < cc.length; i++) h = (h * 31 + cc.charCodeAt(i)) | 0;
+  for (let i = 0; i < key.length; i++) h = (h * 31 + key.charCodeAt(i)) | 0;
   return COST_CENTRE_PALETTE[Math.abs(h) % COST_CENTRE_PALETTE.length];
 }
 // Pastel tint of a #rrggbb colour — blended toward white. Used for recently-
@@ -714,6 +757,27 @@ function applyLiveFilters() {
   });
   speeds.sort((a, b) => a - b);
   renderLiveKPIs({ total: filtered.length, moving, parked, offline, median: speeds.length ? speeds[Math.floor(speeds.length / 2)] : null, last_batch_utc: lastLivePayload?.summary?.last_batch_utc });
+  renderLegend(filtered);
+}
+
+// Compact colour key — lists only the cost centres currently on the map (respects
+// the active filter), sorted by count. Rebuilt on every live render so it stays
+// in sync. Collapsed by default; toggled by the "Key" pill.
+function renderLegend(features) {
+  const body = document.getElementById('legend-body');
+  const wrap = document.getElementById('legend');
+  if (!body || !wrap) return;
+  const counts = new Map();
+  (features || []).forEach(f => {
+    const key = ((f.properties && f.properties.cost_centre) || '').trim() || '(none)';
+    counts.set(key, (counts.get(key) || 0) + 1);
+  });
+  const rows = [...counts.entries()].sort((a, b) => b[1] - a[1]);
+  wrap.style.display = rows.length ? '' : 'none';
+  body.innerHTML = rows.map(([cc, n]) => {
+    const color = cc === '(none)' ? UNKNOWN_CC_COLOR : colorForCostCentre(cc);
+    return `<div class="legend-row"><span class="legend-dot" style="background:${color}"></span><span class="legend-lbl">${escapeHtml(cc)}</span><span class="legend-n">${n}</span></div>`;
+  }).join('');
 }
 
 // Query the cluster index for the current viewport+zoom and draw either count
@@ -1396,6 +1460,9 @@ function backToLive() {
   startPolling();
 }
 document.getElementById('live-pill').addEventListener('click', backToLive);
+document.getElementById('legend-toggle').addEventListener('click', () => {
+  document.getElementById('legend').classList.toggle('collapsed');
+});
 
 // ============================================================================
 // Reverse-geocoding (Nominatim) — queued, 1 req/sec, in-memory cache