Property updates switching between PlatformColors would no-op

[acoates-ms]

Description

In our HostPlatformColor object we had a bool that was representing an undefined color. There were a couple of places where we were treating this bool as isDefined, instead of isUndefined. This caused the == operator of Color to return true when comparing any PlatformColors. - Which causes various issues.

With the following component, the text would not change color when pressing the button:

const Bootstrap = () => {
  const [isHighlight, setIsHighlight] = React.useState(false);
  const swapColors = () => {
    setIsHighlight(!isHighlight);
  };
  return (
    <View>
      <Button title="Press" onPress={swapColors} />
      <Text
        style={{
          color: isHighlight ? PlatformColor('Highlight') : PlatformColor('WindowText'),
        }}>
        <Text>Text here</Text>
      </Text>
    </View>
  );
};

I just removed the whole m_isUndefined property. It is not needed as SharedColor has a bool operator that just compares the color to the global Undefined color, which doesn't need an additional bool.

Microsoft Reviewers: Open in CodeFlow