diff --git a/apps/web/index.html b/apps/web/index.html
index a6d6327..2afd1bc 100644
--- a/apps/web/index.html
+++ b/apps/web/index.html
@@ -3,8 +3,22 @@
   <head>
     <meta charset="UTF-8" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
-    <meta name="color-scheme" content="dark" />
+    <!-- 本期仅浅色主题（Cloud Blue）：声明 light，避免浏览器在样式加载前按深色绘制画布导致黑屏 -->
+    <meta name="color-scheme" content="light" />
     <title>灵犀 · 信息流素材生产平台</title>
+    <!-- 首屏兜底：样式表与 JS 就绪前先铺应用底色，避免默认画布（黑/白）闪烁 -->
+    <style>
+      html,
+      body {
+        color-scheme: light;
+        /* 与 packages/ui/src/theme/tokens.css 的 --lx-color-bg-app 保持一致 */
+        background-color: #f5f7fa;
+      }
+
+      body {
+        margin: 0;
+      }
+    </style>
   </head>
   <body theme-mode="light">
     <div id="root"></div>
diff --git a/apps/web/src/shell.spec.ts b/apps/web/src/shell.spec.ts
new file mode 100644
index 0000000..bb4eee7
--- /dev/null
+++ b/apps/web/src/shell.spec.ts
@@ -0,0 +1,26 @@
+import { readFileSync } from 'node:fs';
+
+import { describe, expect, it } from 'vitest';
+
+/** 从 spec 所在目录解析仓库内文件，避免依赖测试运行目录 */
+function readRepoFile(relativePath: string): string {
+  return readFileSync(new URL(relativePath, import.meta.url), 'utf8');
+}
+
+/** HTML 外壳不支持暗色模式：深色 color-scheme 会让浏览器在样式加载前画黑屏 */
+describe('HTML 外壳首屏防闪烁', () => {
+  const html = readRepoFile('../index.html');
+  const tokens = readRepoFile('../../../packages/ui/src/theme/tokens.css');
+
+  it('只声明浅色 color-scheme，不声明 dark', () => {
+    expect(html).not.toMatch(/name="color-scheme"\s+content="dark"/);
+    expect(html).toMatch(/name="color-scheme"\s+content="light"/);
+    expect(html).toMatch(/color-scheme:\s*light/);
+  });
+
+  it('预置的应用底色与主题 token 一致', () => {
+    const appBackground = /--lx-color-bg-app:\s*(#[0-9a-fA-F]{6})/.exec(tokens)?.[1] ?? '';
+    expect(appBackground).not.toBe('');
+    expect(html.toLowerCase()).toContain(`background-color: ${appBackground.toLowerCase()}`);
+  });
+});
diff --git a/packages/ui/src/theme/tokens.css b/packages/ui/src/theme/tokens.css
index ac41160..eb0c2dc 100644
--- a/packages/ui/src/theme/tokens.css
+++ b/packages/ui/src/theme/tokens.css
@@ -1,4 +1,7 @@
 :root {
+  /* 本期仅浅色主题（Cloud Blue），不提供暗色模式；锁定浅色方案，避免系统深色偏好影响表单控件与滚动条 */
+  color-scheme: light;
+
   /* 方向 A · 云白蓝（Cloud Blue）：传统企业后台骨架 + 现代浅色质感 */
   --lx-color-bg-app: #f5f7fa;
   --lx-color-bg-panel: #ffffff;