--- a/browser/themes/shared/tabs.inc.css
+++ b/browser/themes/shared/tabs.inc.css
@@ -188,23 +188,32 @@ tabbrowser {
 @keyframes tab-throbber-animation {
   100% { transform: translateX(-100%); }
 }
 
 @keyframes tab-throbber-animation-rtl {
   100% { transform: translateX(100%); }
 }
 
+#TabsToolbar[brighttext] .tab-throbber[busy]:not([visuallyselected=true])::before {
+  /* Don't change the --tab-loading-fill variable because this should only affect
+     tabs that are not visually selected. */
+  fill: #717171;
+  opacity: 1;
+}
+
 :root[sessionrestored] .tab-throbber[progress]::before {
   fill: var(--tab-loading-fill);
   opacity: 1;
 }
 
-#TabsToolbar[brighttext] .tabbrowser-tab:not([visuallyselected=true]) {
-  --tab-loading-fill: #bbbbff;
+#TabsToolbar[brighttext] .tab-throbber[progress]:not([visuallyselected=true])::before {
+  /* Don't change the --tab-loading-fill variable because this should only affect
+     tabs that are not visually selected. */
+  fill: #84c1ff;
 }
 
 #tabbrowser-tabs[schedulepressure] .tab-throbber,
 #tabbrowser-tabs:not([schedulepressure]) .tab-throbber-fallback {
   display: none;
 }
 
 .tab-icon-image {