How can I know if a given string is hex, rgb, rgba or hsl color using javascript/jquery?

There are different options here:

1. Use a dummy element

Use the browser's validation. Create a dummy HTML element, assign the color and check if it's set. This is by far the best option. It's not only easier, but it will also allow forward compatibility.

function CheckValidColor(color) {
    var e = document.getElementById('divValidColor');
    if (!e) {
        e = document.createElement('div');
        e.id = 'divValidColor';
    }
    e.style.borderColor = '';
    e.style.borderColor = color;
    var tmpcolor = e.style.borderColor;
    if (tmpcolor.length == 0) {
        return false;
    }
    return true;
}

// function call
var inputOK = CheckValidColor('rgb( 0, 0, 255)');

This will return true for all colors accepted by the browser, even in cases you may consider invalid.

2. Capture the numbers with regex and validate in code

If you capture anything that looks like a number, you will be able to validate each parameter individually with IF clauses. This will allow you to provide better feedback to the user.

a) #hex:

^(#)((?:[A-Fa-f0-9]{3}){1,2})$

The hash is also captured for consistency with the following expression. DEMO

b) rgb(), rgba(), hsl() and hsla():

^(rgb|hsl)(a?)[(]\s*([\d.]+\s*%?)\s*,\s*([\d.]+\s*%?)\s*,\s*([\d.]+\s*%?)\s*(?:,\s*([\d.]+)\s*)?[)]$

This will create captures for the function and each parameter. DEMO

3. Validate with one monster regex:

This option is not recommended, mainly because it's quite difficult to read, it won't guarantee to match all use cases, and it will give you a headache if you try to debug it. The following regex validates the number of parameters allowed and ranges.

a) #hex: ^#(?:[A-Fa-f0-9]{3}){1,2}$ DEMO

b) rgb(): ^rgb[(](?:\s*0*(?:\d\d?(?:\.\d+)?(?:\s*%)?|\.\d+\s*%|100(?:\.0*)?\s*%|(?:1\d\d|2[0-4]\d|25[0-5])(?:\.\d+)?)\s*(?:,(?![)])|(?=[)]))){3}[)]$ DEMO

c) rgba(): ^^rgba[(](?:\s*0*(?:\d\d?(?:\.\d+)?(?:\s*%)?|\.\d+\s*%|100(?:\.0*)?\s*%|(?:1\d\d|2[0-4]\d|25[0-5])(?:\.\d+)?)\s*,){3}\s*0*(?:\.\d+|1(?:\.0*)?)\s*[)]$ DEMO

d) hsl(): ^hsl[(]\s*0*(?:[12]?\d{1,2}|3(?:[0-5]\d|60))\s*(?:\s*,\s*0*(?:\d\d?(?:\.\d+)?\s*%|\.\d+\s*%|100(?:\.0*)?\s*%)){2}\s*[)]$ DEMO

e) hsla(): ^hsla[(]\s*0*(?:[12]?\d{1,2}|3(?:[0-5]\d|60))\s*(?:\s*,\s*0*(?:\d\d?(?:\.\d+)?\s*%|\.\d+\s*%|100(?:\.0*)?\s*%)){2}\s*,\s*0*(?:\.\d+|1(?:\.0*)?)\s*[)]$ DEMO

All toghether now:

With the above expressions, we can create this one-liner to validate all legal color values:

^(?:#(?:[A-Fa-f0-9]{3}){1,2}|(?:rgb[(](?:\s*0*(?:\d\d?(?:\.\d+)?(?:\s*%)?|\.\d+\s*%|100(?:\.0*)?\s*%|(?:1\d\d|2[0-4]\d|25[0-5])(?:\.\d+)?)\s*(?:,(?![)])|(?=[)]))){3}|hsl[(]\s*0*(?:[12]?\d{1,2}|3(?:[0-5]\d|60))\s*(?:\s*,\s*0*(?:\d\d?(?:\.\d+)?\s*%|\.\d+\s*%|100(?:\.0*)?\s*%)){2}\s*|(?:rgba[(](?:\s*0*(?:\d\d?(?:\.\d+)?(?:\s*%)?|\.\d+\s*%|100(?:\.0*)?\s*%|(?:1\d\d|2[0-4]\d|25[0-5])(?:\.\d+)?)\s*,){3}|hsla[(]\s*0*(?:[12]?\d{1,2}|3(?:[0-5]\d|60))\s*(?:\s*,\s*0*(?:\d\d?(?:\.\d+)?\s*%|\.\d+\s*%|100(?:\.0*)?\s*%)){2}\s*,)\s*0*(?:\.\d+|1(?:\.0*)?)\s*)[)])$

DEMO

Or the regex enthusiasts can check this huge regex, with 148 color names. But I would never recommend using that pattern. Please use the first option, creating a dummy element, which is the only way to cover all use cases for the browser.

I dont know about other browsers but in chrome the color will only be set if its valid:

var isValidColor = function(color) {
  var el = document.createElement('div');
  el.style.backgroundColor = color;
  return el.style.backgroundColor ? true : false;
};

console.log(isValidColor('#ff0000')); // true
console.log(isValidColor('rgb(0, 0)')); // false

It will have it's pitfalls though, because Chrome will do auto rounding of numbers:

// 0, 0, 256 is not a valid color, but this says yes
console.log(isValidColor('rgb(0, 0, 256)')); // true