 method, use
    // DiagnosticsProperty&lt;YourValueType&gt;. Specifying the value type ensures
    // that debugging tools always know the type of the field and so can
    // provide the right UI affordances. For example, in this case even
    // if color is null, a debugging tool still knows the value is a Color
    // and can display relevant color related UI.
    properties.add(DiagnosticsProperty&lt;Color&gt;('color', color));

    // Use a custom description to generate a more terse summary than the
 