diff --git a/frontend/src/features/agents/CustomAgentChatView.test.tsx b/frontend/src/features/agents/CustomAgentChatView.test.tsx
index 480ef894..0fef93de 100644
--- a/frontend/src/features/agents/CustomAgentChatView.test.tsx
+++ b/frontend/src/features/agents/CustomAgentChatView.test.tsx
@@ -212,16 +212,19 @@ describe("CustomAgentChatView", () => {
     const watermark = await screen.findByTestId("project-icon-watermark");
     expect(watermark.style.pointerEvents).toBe("none");
     expect(watermark.getAttribute("aria-hidden")).toBe("true");
-    expect((watermark.firstElementChild as HTMLElement | null)?.style.width).toBe("92%");
-    expect((watermark.firstElementChild as HTMLElement | null)?.style.height).toBe("92%");
+    expect(watermark.className).toContain("project-cell-illustration");
+    expect((watermark.firstElementChild as HTMLElement | null)?.style.width).toBe("100%");
+    expect((watermark.firstElementChild as HTMLElement | null)?.style.height).toBe("100%");
+    expect((watermark.firstElementChild as HTMLElement | null)?.className).toContain("project-cell-illustration__glyph");
     expect(watermark.textContent).toBe("🐍\uFE0E");
     expect(watermark.dataset.colorMode).toBe("monochrome");
+    expect(watermark.style.getPropertyValue("--project-illustration-tint")).toBe("var(--color-muted, #9aa7b4)");
     publishProjectIconChanged({ projectId: "project-1", icon: { set: "emoji", name: "star" } });
     await waitFor(() => expect(watermark.textContent).toBe("⭐\uFE0E"));
     publishProjectThemeChanged({ projectId: "project-1", themeColor: "#7c3aed" });
     await waitFor(() => {
       expect(watermark.dataset.colorMode).toBe("project");
-      expect(watermark.style.color).toBe("rgb(124, 58, 237)");
+      expect(watermark.style.getPropertyValue("--project-illustration-tint")).toBe("#945DF0");
     });
     expect(screen.getByTestId("custom-agent-chat-scroll").className).toContain("z-10");
     expect(screen.getByTestId("custom-agent-chat-composer").className).toContain("bg-raised/40");
diff --git a/frontend/src/features/agents/CustomAgentChatView.tsx b/frontend/src/features/agents/CustomAgentChatView.tsx
index ceb45662..366a5004 100644
--- a/frontend/src/features/agents/CustomAgentChatView.tsx
+++ b/frontend/src/features/agents/CustomAgentChatView.tsx
@@ -15,6 +15,7 @@ import {
   useRef,
   useState,
   type ClipboardEvent,
+  type CSSProperties,
   type KeyboardEvent,
   type MouseEvent as ReactMouseEvent,
   type RefObject,
@@ -45,7 +46,11 @@ import {
 } from "@/features/projects/projectCliInteractionActivity";
 import { Button, EntryTimestamp, Spinner, cn, normalizeTimestamp } from "@/shared";
 import { onProjectIconChanged, ProjectIcon } from "@/features/projects/projectIcons";
-import { onProjectThemeChanged, validThemeColor } from "@/features/projects/projectTheme";
+import {
+  accessibleProjectAccent,
+  onProjectThemeChanged,
+  validThemeColor,
+} from "@/features/projects/projectTheme";
 import type {
   ChatAttachmentInput,
   ChatDraftScope,
@@ -2504,26 +2509,28 @@ export function CustomAgentChatView({
     <div
       ref={chatRootRef}
       data-testid="custom-agent-chat-view"
-      className="relative z-0 flex h-full min-h-0 flex-col overflow-hidden bg-surface text-content"
+      className="custom-agent-chat-view relative z-0 flex h-full min-h-0 flex-col overflow-hidden bg-surface text-content"
     >
       <div
         data-testid="project-icon-watermark"
         data-color-mode={projectThemeColor ? "project" : "monochrome"}
         aria-hidden="true"
-        className="pointer-events-none absolute inset-0 z-0 flex items-center justify-center overflow-hidden text-content opacity-[0.055]"
+        className="project-cell-illustration pointer-events-none absolute z-0 flex items-center justify-center overflow-hidden"
         style={{
           pointerEvents: "none",
-          containerType: "size",
-          color: projectThemeColor ?? undefined,
-        }}
+          "--project-illustration-tint": projectThemeColor
+            ? accessibleProjectAccent(projectThemeColor)
+            : "var(--color-muted, #9aa7b4)",
+        } as CSSProperties}
       >
         <ProjectIcon
           icon={projectIcon}
           fallbackLabel={projectFallbackLabel}
           surface="watermark"
-          size="92%"
+          size="100%"
           decorative
-          style={{ fontSize: "min(34cqw, 34cqh)", maxWidth: "92cqh", maxHeight: "92cqw" }}
+          className="project-cell-illustration__glyph"
+          style={{ fontSize: "min(88cqw, 88cqh)" }}
         />
       </div>
       <div
@@ -2727,7 +2734,7 @@ export function CustomAgentChatView({
             </div>
           </div>
         ) : displayTurns.length === 0 ? (
-          <p className="m-auto text-xs text-muted">
+          <p className="project-cell-empty-label text-xs text-muted">
             {t("custom.empty")}
           </p>
         ) : (
diff --git a/frontend/src/shared/styles/theme.css b/frontend/src/shared/styles/theme.css
index 11406731..76fa0f02 100644
--- a/frontend/src/shared/styles/theme.css
+++ b/frontend/src/shared/styles/theme.css
@@ -103,6 +103,51 @@
 }
 
 @layer components {
+  .custom-agent-chat-view {
+    container-type: size;
+  }
+
+  .project-cell-illustration {
+    inset: 6px 4px;
+    color: transparent;
+    opacity: 0.045;
+  }
+
+  .project-cell-illustration[data-color-mode="project"] {
+    opacity: 0.065;
+  }
+
+  /* Emoji fonts may ignore the text-variation selector and retain their own
+     palette. Painting a zero-offset text shadow through the glyph alpha mask
+     guarantees one semantic project tint without depending on the host font. */
+  .project-cell-illustration__glyph {
+    color: transparent;
+    -webkit-text-fill-color: transparent;
+    text-shadow: 0 0 0 var(--project-illustration-tint, var(--color-muted));
+  }
+
+  .project-cell-empty-label {
+    position: relative;
+    z-index: 1;
+    max-width: min(34rem, 88%);
+    margin: auto auto 8px;
+    text-align: center;
+  }
+
+  /* Preserve the illustration when a split cell becomes constrained; the
+     explanatory copy is the first element to yield. */
+  @container (max-width: 280px) {
+    .project-cell-empty-label {
+      display: none;
+    }
+  }
+
+  @container (max-height: 240px) {
+    .project-cell-empty-label {
+      display: none;
+    }
+  }
+
   .stopped-agent-cell {
     position: absolute;
     inset: 0;