diff --git a/polygerrit-ui/app/elements/change/gr-message/gr-message.ts b/polygerrit-ui/app/elements/change/gr-message/gr-message.ts
index 39cdf22..2fe409a 100644
--- a/polygerrit-ui/app/elements/change/gr-message/gr-message.ts
+++ b/polygerrit-ui/app/elements/change/gr-message/gr-message.ts
@@ -40,6 +40,7 @@
   NumericChangeId,
   ChangeMessageId,
   PatchSetNum,
+  AccountInfo,
 } from '../../../types/common';
 import {CommentThread} from '../../../utils/comment-util';
 import {hasOwnProperty} from '../../../utils/common-util';
@@ -51,6 +52,7 @@
   computeLatestPatchNum,
   computePredecessor,
 } from '../../../utils/patch-set-util';
+import {isServiceUser} from '../../../utils/account-util';
 
 const PATCH_SET_PREFIX_PATTERN = /^(?:Uploaded\s*)?(?:P|p)atch (?:S|s)et \d+:\s*(.*)/;
 const LABEL_TITLE_SCORE_PATTERN = /^(-?)([A-Za-z0-9-]+?)([+-]\d+)?[.]?$/;
@@ -472,9 +474,10 @@
     return classes.join(' ');
   }
 
-  _computeClass(expanded: boolean) {
+  _computeClass(expanded?: boolean, author?: AccountInfo) {
     const classes = [];
     classes.push(expanded ? 'expanded' : 'collapsed');
+    if (isServiceUser(author)) classes.push('serviceUser');
     return classes.join(' ');
   }
 
diff --git a/polygerrit-ui/app/elements/change/gr-message/gr-message_html.ts b/polygerrit-ui/app/elements/change/gr-message/gr-message_html.ts
index 0409a42..b93040b 100644
--- a/polygerrit-ui/app/elements/change/gr-message/gr-message_html.ts
+++ b/polygerrit-ui/app/elements/change/gr-message/gr-message_html.ts
@@ -39,11 +39,24 @@
     .contentContainer {
       padding: var(--spacing-m) var(--spacing-l);
     }
+    .expanded .contentContainer {
+      background-color: var(--background-color-secondary);
+    }
     .collapsed .contentContainer {
-      /* For expanded state we inherit the alternating background color
-           that is set in gr-messages-list. */
       background-color: var(--background-color-primary);
     }
+    div.serviceUser.expanded div.contentContainer {
+      background-color: var(
+        --background-color-service-user,
+        var(--background-color-secondary)
+      );
+    }
+    div.serviceUser.collapsed div.contentContainer {
+      background-color: var(
+        --background-color-service-user,
+        var(--background-color-primary)
+      );
+    }
     .name {
       font-weight: var(--font-weight-bold);
     }
@@ -188,7 +201,7 @@
       }
     }
   </style>
-  <div class$="[[_computeClass(_expanded)]]">
+  <div class$="[[_computeClass(_expanded, author)]]">
     <div class="contentContainer">
       <div class="author" on-click="_handleAuthorClick">
         <span hidden$="[[!showOnBehalfOf]]">
diff --git a/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list_html.ts b/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list_html.ts
index e1ef3f8..6c786ef 100644
--- a/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list_html.ts
+++ b/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list_html.ts
@@ -50,9 +50,6 @@
     gr-message:not(:last-of-type) {
       border-bottom: 1px solid var(--border-color);
     }
-    gr-message {
-      background-color: var(--background-color-secondary);
-    }
   </style>
   <div class="header">
     <div id="showAllActivityToggleContainer" class="container">