Failed to convert @color/Blue into a drawable when setting background color

Question

res/layout/activity_main.xml

<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
android:background="@color/Blue">

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
     />
</RelativeLayout>

meanwhile, res/values/colors.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
<color name="Blue">#0000FF</color>
</resources>

as you can see, the color does start with #

The code is exactly as you see it.

Answer 1

I have to go to File-->Invalidate Cache/Restart.

It amazes me that this bug still hasn't been fixed in Android Studio, searching on SO it looks like it has plagued other people in different ways.