Somehow in the excitement around HTML5’s new input types I missed the addition of an input type specifically for selecting colours:

<input type="color">

Include this and you’ll get a platform-native colour selector that takes and returns hex colour values, like my debugging colour of choice #ff0099:

Selecting colours in HTML vGogBW

Note that the value needs to a fully hex string, not a shortcut like #f09. And, alas, if you’re viewing this in Safari you’ll notice that it isn’t supported at all.