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function convertRGBtoHEX(rgbString) {

    var parts = rgbString.match(/^rgb\((\d+),\s*(\d+),\s*(\d+)\)$/);
    // parts now should be ["rgb(0, 70, 255", "0", "70", "255"]

    delete (parts[0]);
    for (var i = 1; i <= 3; ++i) {
        parts[i] = parseInt(parts[i]).toString(16);
        if (parts[i].length == 1) parts[i] = '0' + parts[i];
    }
    var hexString = '#' + parts.join('').toUpperCase(); // "#0070FF"

    return hexString;

}