ContrastToolBar.qml

import QtQuick 2.10
import QtQuick.Controls 2.3
import QtQuick.Controls.Material 2.3

ToolBar {
    id: _contrastToolBar

    height: 56

    function accentTextColor(accentColor, baseColor) {
        var a = (0.299 * accentColor.r + 0.587 * accentColor.g + 0.144 * accentColor.b);
        if(typeof baseColor !== "undefined") {
            var b = (0.299 * baseColor.r + 0.587 * baseColor.g + 0.144 * baseColor.b);
            if (Math.abs(a - b) >= 0.5)
                return baseColor;
        }
        if(a < 0.5)
            return "#FFFFFF";
        else
            return "#000000";
    }

    Material.foreground: accentTextColor(Material.primary)
}