Tune colors for accessibility

<resources>

    <!-- Default background color for the status bar. -->

    <color name="calculator_accent_color">#00BCD4</color>

    <color name="calculator_accent_color">#0097A7</color>

    <!-- Color to indicate an error has occured. -->

    <color name="calculator_error_color">#F40056</color>

    <color name="calculator_error_color">#C2185B</color>

    <!-- Background color of the calculator display. -->

    <color name="display_background_color">#FFF</color>