Change SolidColor

I am triyng to change the color of a button with a trigger but I cant get work. How can I change the color if is set with a Solid Color like:

<Button Focus.IsFocusable="true">

<SolidColor Color="0,0,0,1" />

 <Tapped>
     <GiveFocus />
 </Tapped>

 <Focusing>

 </Focusing>

 </Button>

This is from my head, but I think you can do:

<Button Focus.IsFocusable="true">

    <Rectangle ux:Binding="Appearance">
        <SolidColor Color="0,0,0,1" ux:Name="bgColor" />
    </Rectangle>

    <Tapped>
        <GiveFocus />
    </Tapped>

    <Focusing>
        <Change Target="bgColor.Color" Value="#345" />
    </Focusing>

</Button>

You can also drop focus like this:

<Button>
    <SolidColor Color="0,0,0,1" ux:Name="bgColor" />
    <Pressing>
        <Change Target="bgColor.Color" Value="#345" />
    </Pressing>
</Button>

Thanks! Works great!