material.io is a free, no trick, easy grab, palette tool that will allow you compose your color harmony for Android and iOS in a very simplistic way.
This website is based on Material Design, which is a design language developed by Google. Very popular across the board.
https://material.io/resources/color here you may find a large array of colors and easily generate primaryColor, primaryLightColor, primaryDarkColor, secondaryColor, primaryTextColor, etc.
On top of that, it will allow you to download straightaway a colors.xml or colors.xml file with all the constants well defined, which is pretty convenient. Ready to drop into your Android Studio or XCode project.