JavaScript Colour Converter
Nice code, only a few comments to offer here:

.1.

var rgb = document.getElementById("rgb");
var rgb2 = document.getElementById("rgb2");
var rgb3 = document.getElementById("rgb3");


This way of keeping the r, g, and b is not the best. Consider having to keep six of them, or more. You would not do this that way. You cannot run a loop with this and this gets obvious in 

    if (rgb.value.length &gt;= this.maxLength) {
        rgb2.focus();
    }
    if (rgb2.value.length &gt;= this.maxLength) {
        rgb3.focus();
    }


So what I would do is:

var getEl = document.getElementById;
var rgbElements = {
                   r:getEl("rgb"),
                   g:getEl("rgb2"),
                   b:getEl("rgb3")
                  }


This way you could run a loop for these.

.2.
This code

document.getElementById("hex").addEventListener("input", function() {
    // Sets colours for SVG, picker, converts HEX to RGB and prints out HEX
    svgPath.style.fill = '#' + this.value;
    colorInput.value = '#' + this.value;
    hexOutput.innerHTML = 'HEX: #' + this.value.toUpperCase();
    rgbOutput.innerHTML = 'RGB: rgb(' + hexToRGB(this.value) + ')';
}, false);


should be like this one

document.getElementById("hex").addEventListener("input", function() {
    // Sets colours for SVG, picker, converts HEX to RGB and prints out HEX
    var hexVal = this.value;
    svgPath.style.fill = '#' + hexVal;
    colorInput.value = '#' + hexVal;
    hexOutput.innerHTML = 'HEX: #' + hexVal.toUpperCase();
    rgbOutput.innerHTML = 'RGB: rgb(' + hexToRGB(hexVal) + ')';
}, false);


You should not 'ask' for values from 'this' or higher scope when you can have it closer.