SOURCE

function toFixed(a, fix = 4) {
    const str = `${a}`
    if (/^(\d+)(\.\d+)?/i.test(str)) {
        const left = RegExp.$1
        const right = RegExp.$2.slice(1, Math.min(fix, RegExp.$2.length - 1) + 1)
        const final = [left, right].filter(Boolean).join('.')
        return Number(final)
    }
    return ''
}

function getHex(a) {
    let cur = toFixed(a)
    let hex = 0x00
    while(hex <= 0xff) {
        let tmp = toFixed(hex / 255)
        if (tmp == cur) {
            break
        } 
        hex += 1
    }
    return hex.toString(16)
}

function getRgb(str) {
    let red = 0
    let green = 0
    let blue = 0
    if (/red\="(\d+(?:\.\d+)?)"/i.test(str)) {
        red = getHex(RegExp.$1)
    }
    if (/green\="(\d+(?:\.\d+)?)"/i.test(str)) {
        green = getHex(RegExp.$1)
    }
    if (/blue\="(\d+(?:\.\d+)?)"/i.test(str)) {
        blue = getHex(RegExp.$1)
    }
    return `#${red}${green}${blue}`
}
console.log(getRgb('red="0.20000000000000001" green="0.20000000000000001" blue="0.20000000000000001"'))