Get colors working.

packages/codemirror/src/editor.ts

@@ -751,8 +751,9 @@ class CodeMirrorEditor implements CodeEditor.IEditor {
     let name = collaborator ? collaborator.displayName : 'Anonymous';
     let color = collaborator ? collaborator.color : this._selectionStyle.color;
     let caret: HTMLElement = document.createElement('span');
-    caret.dataset.name = name;
+    caret.dataset.name = name; // Allows getting from :after element.
     caret.className = `jp-CollaboratorCursor`;
+    caret.style.backgroundColor = color; // Allows inheritence in :after element.
     caret.style.borderBottomColor = color;
     return caret;
   }

packages/codemirror/style/index.css

@@ -71,6 +71,7 @@
   border-right: 5px solid transparent;
   border-top: none;
   border-bottom: 3px solid;
+  background-clip: content-box;
   margin-left: -5px;
   margin-right: -5px;
 }
@@ -80,7 +81,7 @@
   position: absolute;
   z-index: 1;
   transform: translateX(-50%) translateY(100%);
-  background-color: var(--jp-brand-color2);
+  background-color: inherit;
   color: white;
   border-radius: 3px;
   padding: 1px;