diff --git a/ui/src/components/ContributionGraph.tsx b/ui/src/components/ContributionGraph.tsx
index a1a47f1..6250b90 100644
--- a/ui/src/components/ContributionGraph.tsx
+++ b/ui/src/components/ContributionGraph.tsx
@@ -2,7 +2,7 @@ import { useMemo } from 'react';
 import { useQuery } from '@tanstack/react-query';
 import { useNavigate } from 'react-router-dom';
 
-import { fetchDailyCounts, fetchProjects, fetchSources } from '../api/client';
+import { fetchDailyCounts, fetchLanguageDailyCounts, fetchProjects, fetchSources } from '../api/client';
 
 const CELL_SIZE = 12;
 const GAP = 3;
@@ -14,13 +14,8 @@ const TOP_LABEL_HEIGHT = 16;
 const DAY_LABELS = ['', 'mon', '', 'wed', '', 'fri', ''];
 const MONTH_LABELS = ['jan', 'feb', 'mar', 'apr', 'may', 'jun', 'jul', 'aug', 'sep', 'oct', 'nov', 'dec'];
 
-const COLORS = [
-  'rgba(255,255,255,0.05)',
-  '#0e4429',
-  '#006d32',
-  '#26a641',
-  '#39d353',
-];
+const EMPTY_COLOR = 'rgba(255,255,255,0.05)';
+const FALLBACK_COLOR = '#39d353';
 
 /** Daily contribution graph — last 1 year, one circle per day. */
 export function ContributionGraph() {
@@ -37,6 +32,12 @@ export function ContributionGraph() {
     staleTime: 5 * 60_000,
   });
 
+  const langQ = useQuery({
+    queryKey: ['language-daily', fromStr, toStr],
+    queryFn: () => fetchLanguageDailyCounts(fromStr, toStr),
+    staleTime: 5 * 60_000,
+  });
+
   const projectsQ = useQuery({
     queryKey: ['projects'],
     queryFn: fetchProjects,
@@ -56,6 +57,11 @@ export function ContributionGraph() {
 
   const navigate = useNavigate();
 
+  // Build map of date → dominant language color
+  const dayColorMap = useMemo(() => {
+    return buildDominantColorMap(langQ.data ?? []);
+  }, [langQ.data]);
+
   const { weeks, monthMarkers, thresholds, totalCount } = useMemo(() => {
     const counts = dailyQ.data ?? [];
     const countMap = new Map(counts.map((d) => [d.date, d.count]));
@@ -142,7 +148,8 @@ export function ContributionGraph() {
                 cx={LEFT_LABEL_WIDTH + col * (CELL_SIZE + GAP) + RADIUS}
                 cy={TOP_LABEL_HEIGHT + row * (CELL_SIZE + GAP) + RADIUS}
                 r={RADIUS - 1}
-                fill={colorFor(count, thresholds)}
+                fill={count === 0 ? EMPTY_COLOR : (dayColorMap.get(date) ?? FALLBACK_COLOR)}
+                opacity={count === 0 ? 1 : opacityFor(count, thresholds)}
                 className="graph-cell"
                 onClick={() => navigate(`/activity/${date}`)}
               >
@@ -192,8 +199,42 @@ export function AllTimeGraph() {
     staleTime: 10 * 60_000,
   });
 
+  const langQ = useQuery({
+    queryKey: ['language-daily-alltime', fromStr, toStr],
+    queryFn: () => fetchLanguageDailyCounts(fromStr, toStr),
+    enabled: !!earliest,
+    staleTime: 10 * 60_000,
+  });
+
   const navigate = useNavigate();
 
+  // Aggregate daily language data to month level: pick the language with most commits
+  const monthColorMap = useMemo(() => {
+    const entries = langQ.data ?? [];
+    if (entries.length === 0) return new Map<string, string>();
+    const map = new Map<string, Map<string, { commits: number; color: string }>>();
+    for (const e of entries) {
+      const key = e.date.slice(0, 7); // YYYY-MM
+      if (!map.has(key)) map.set(key, new Map());
+      const langMap = map.get(key)!;
+      const cur = langMap.get(e.language);
+      if (cur) {
+        cur.commits += e.commits;
+      } else {
+        langMap.set(e.language, { commits: e.commits, color: e.color ?? FALLBACK_COLOR });
+      }
+    }
+    const result = new Map<string, string>();
+    for (const [key, langMap] of map) {
+      let best = { commits: 0, color: FALLBACK_COLOR };
+      for (const v of langMap.values()) {
+        if (v.commits > best.commits) best = v;
+      }
+      result.set(key, best.color);
+    }
+    return result;
+  }, [langQ.data]);
+
   const { years, monthGrid, thresholds, totalCount } = useMemo(() => {
     const counts = dailyQ.data ?? [];
     if (counts.length === 0) return { years: [], monthGrid: [], thresholds: [1, 2, 3], totalCount: 0 };
@@ -206,15 +247,16 @@ export function AllTimeGraph() {
     for (let yr = startYear; yr <= endYear; yr++) years.push(yr);
 
     // Build a 12 x years grid of monthly totals
-    const monthGrid: { year: number; month: number; count: number; monthStart: string; monthEnd: string }[][] = [];
+    const monthGrid: { year: number; month: number; count: number; monthStart: string; monthEnd: string; monthKey: string }[][] = [];
     for (let m = 0; m < 12; m++) {
       const row: typeof monthGrid[0] = [];
       for (const yr of years) {
         const monthStart = new Date(yr, m, 1);
         const monthEnd = new Date(yr, m + 1, 0); // last day of month
+        const monthKey = `${yr}-${String(m + 1).padStart(2, '0')}`;
         // Don't include months entirely outside our data range
         if (monthStart > to || monthEnd < from) {
-          row.push({ year: yr, month: m, count: 0, monthStart: fmt(monthStart), monthEnd: fmt(monthEnd) });
+          row.push({ year: yr, month: m, count: 0, monthStart: fmt(monthStart), monthEnd: fmt(monthEnd), monthKey });
           continue;
         }
         let total = 0;
@@ -223,7 +265,7 @@ export function AllTimeGraph() {
           total += countMap.get(fmt(cursor)) ?? 0;
           cursor.setDate(cursor.getDate() + 1);
         }
-        row.push({ year: yr, month: m, count: total, monthStart: fmt(monthStart), monthEnd: fmt(monthEnd) });
+        row.push({ year: yr, month: m, count: total, monthStart: fmt(monthStart), monthEnd: fmt(monthEnd), monthKey });
       }
       monthGrid.push(row);
     }
@@ -281,13 +323,14 @@ export function AllTimeGraph() {
           ))}
           {/* Monthly contribution circles */}
           {monthGrid.map((row, rowIdx) =>
-            row.map(({ year, count, monthStart, monthEnd }, colIdx) => (
+            row.map(({ year, count, monthStart, monthEnd, monthKey }, colIdx) => (
               <circle
                 key={`${year}-${rowIdx}`}
                 cx={monthLabelWidth + colIdx * (CELL_SIZE + GAP) + RADIUS}
                 cy={topLabelHeight + rowIdx * (CELL_SIZE + GAP) + RADIUS}
                 r={RADIUS - 1}
-                fill={colorFor(count, thresholds)}
+                fill={count === 0 ? EMPTY_COLOR : (monthColorMap.get(monthKey) ?? FALLBACK_COLOR)}
+                opacity={count === 0 ? 1 : opacityFor(count, thresholds)}
                 className="graph-cell"
                 onClick={() => navigate(`/activity/${monthStart}..${monthEnd}`)}
               >
@@ -305,12 +348,28 @@ function fmt(d: Date): string {
   return d.toISOString().slice(0, 10);
 }
 
-function colorFor(count: number, thresholds: number[]): string {
-  if (count === 0) return COLORS[0];
-  if (count <= thresholds[0]) return COLORS[1];
-  if (count <= thresholds[1]) return COLORS[2];
-  if (count <= thresholds[2]) return COLORS[3];
-  return COLORS[4];
+/** Build a map of date → dominant (highest commit count) language color. */
+function buildDominantColorMap(entries: { date: string; language: string; color: string | null; commits: number }[]): Map<string, string> {
+  const map = new Map<string, { commits: number; color: string }>();
+  for (const e of entries) {
+    const cur = map.get(e.date);
+    if (!cur || e.commits > cur.commits) {
+      map.set(e.date, { commits: e.commits, color: e.color ?? FALLBACK_COLOR });
+    }
+  }
+  const result = new Map<string, string>();
+  for (const [date, { color }] of map) {
+    result.set(date, color);
+  }
+  return result;
+}
+
+/** Map count to opacity (0.3 – 1.0) based on quartile thresholds. */
+function opacityFor(count: number, thresholds: number[]): number {
+  if (count <= thresholds[0]) return 0.35;
+  if (count <= thresholds[1]) return 0.55;
+  if (count <= thresholds[2]) return 0.75;
+  return 1;
 }
 
 function computeThresholds(sorted: number[]): number[] {