diff --git a/lib/rich-text.test.ts b/lib/rich-text.test.ts
index 2be939d..6a0a2a1 100644
--- a/lib/rich-text.test.ts
+++ b/lib/rich-text.test.ts
@@ -15,6 +15,14 @@ describe("rich text sanitization", () => {
     );
   });
 
+  it("normalizes browser-generated RGB text colors to safe hex colors", () => {
+    expect(sanitizeRichTextHtml(
+      '<p><span style="color: rgb(0, 255, 0);">green</span> <span style="color: rgb(255, 204, 0)">yellow</span></p>',
+    )).toBe(
+      '<p><span style="color: #00FF00">green</span> <span style="color: #FFCC00">yellow</span></p>',
+    );
+  });
+
   it("removes executable markup, unsafe links, and unsupported styles", () => {
     expect(sanitizeRichTextHtml(
       '<script>alert(1)</script><p onclick="bad()">Safe <span style="background:red;color:red">text</span><a href="javascript:bad()">link</a></p>',
diff --git a/lib/rich-text.ts b/lib/rich-text.ts
index ec7978b..7281851 100644
--- a/lib/rich-text.ts
+++ b/lib/rich-text.ts
@@ -22,6 +22,18 @@ const HTML_COMMENT = /<!--[\s\S]*?-->/g;
 const TAG = /<\/?([a-zA-Z][a-zA-Z0-9-]*)([^>]*)>/g;
 const ATTRIBUTE = /([a-zA-Z_:][a-zA-Z0-9_:.-]*)\s*=\s*("[^"]*"|'[^']*'|[^\s"'=<>`]+)/g;
 const HEX_COLOR = /^#[0-9a-fA-F]{6}$/;
+const RGB_COLOR = /^rgb\(\s*(\d{1,3})\s*,\s*(\d{1,3})\s*,\s*(\d{1,3})\s*\)$/i;
+
+function normalizeRichTextColor(value: string): string | null {
+  const color = value.trim();
+  if (HEX_COLOR.test(color)) return color.toUpperCase();
+
+  const rgb = color.match(RGB_COLOR);
+  if (!rgb) return null;
+  const channels = rgb.slice(1).map(Number);
+  if (channels.some((channel) => channel > 255)) return null;
+  return `#${channels.map((channel) => channel.toString(16).padStart(2, "0")).join("")}`.toUpperCase();
+}
 
 export function sanitizeRichTextUrl(value: string): string {
   const url = value.trim();
@@ -75,9 +87,11 @@ export function sanitizeRichTextHtml(value: string): string {
 
       if (name === "span") {
         const style = attributeValue(rawAttributes, "style");
-        const color = style.match(/(?:^|;)\s*color\s*:\s*(#[0-9a-fA-F]{6})\s*(?:;|$)/)?.[1];
-        return color && HEX_COLOR.test(color)
-          ? `<span style="color: ${color.toUpperCase()}">`
+        const color = normalizeRichTextColor(
+          style.match(/(?:^|;)\s*color\s*:\s*([^;]+?)\s*(?:;|$)/i)?.[1] ?? "",
+        );
+        return color
+          ? `<span style="color: ${color}">`
           : "<span>";
       }