Update theme colours for watch type devices.

Bug: 26914376
Change-Id: I127a9404fa8dea2db6c3196742566f8d12ccb113
diff --git a/core/res/res/values-watch/colors_material.xml b/core/res/res/values-watch/colors_material.xml
index 91eee7d..45eb981 100644
--- a/core/res/res/values-watch/colors_material.xml
+++ b/core/res/res/values-watch/colors_material.xml
@@ -20,5 +20,7 @@
     <color name="accent_material_dark">#ff5e97f6</color>
     <color name="accent_material_light">#ff4285f4</color>
 
+    <color name="primary_material_dark">#4D4D4D</color>
+
     <color name="button_material_dark">#ff999999</color>
 </resources>