Make text button color responsive to theme.

app/src/main/res/color/ultramarine_text_button.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <selector xmlns:android="http://schemas.android.com/apk/res/android">
-    <item android:color="@color/core_ultramarine" android:state_enabled="true" />
+    <item android:color="?attr/colorAccent" android:state_enabled="true" />
     <item android:color="?attr/title_text_color_secondary" />
 </selector>