Converting string to function name

Learning React Native. Trying to convert a string into a function name. Getting an error saying "func is not a function. func is undefined". Need some help please. The end objective is to create a view with a background color and having buttons for increasing / decreasing RGB values

  const [red, setRed] = useState(0);
  const [green, setGreen] = useState(0);
  const [blue, setBlue] = useState(0);

  const setColor = (color, change) => {
    // color === "red", "green", "blue"
    // change === +10, -10
    const colorCapitalized = color.charAt(0).toUpperCase() + color.slice(1);
    var stateMethod = 'set' + colorCapitalized;
    var func = window[stateMethod];

    if (color + change > 255 || color + change < 0) {
      return;
    } else {
      func(color + change);
    }
  };