I had the same idea to build a web based graphical design tool: http://upmock.com/earlybird (https://github.com/daleharvey/upmock-client)
It works as a nice demo, but would take a lot of time that I dont have to make it reach really useful quality.
I am hoping a web based tool for graphically designing user interfaces at high fidelity comes around soon, this looks great, and certainly a better start than mine. but its still early days, I would love to see some momentum around contributing to it
For designers looking for something like this that's more finished and ready for use in web design production workflows, and supported, please give my bootstrapped web application Edit Room a serious look: http://www.edit-room.com/
Not only can you create semantic HTML structures and style them with professional design production tools, you can also animate your main blocks of content with visual keyframes and Edit Room generates CSS Animations. Works with both WebKit and Gecko browser engines.
The layout engine is responsive by default, with layout units defined as percentages... Key commands... undo/redo... constant autosave... Webfonts with Typekit integration... and more.
Edit: I'm glad I didn't come off as a dick. Here are some homepages I like:
For others who might be interested (as I am) in using Common.js modules in the browser, browserify ( https://github.com/substack/node-browserify ) does the same thing for Node.js as the sprockets-commonjs used in this project: compiles those modules into a single file for the client. It's especially effective there because you can use the same node_modules on the browser and the server, so you get effortless sharing of code.
For what it’s worth, HSL and HSV (just like the RGB they’re trivially derived from) are both terrible color spaces to be interacting with, as humans. Here’s my fuller explanation why: http://en.wikipedia.org/wiki/HSL_and_HSV#Disadvantages. That they’ve been enshrined places like the CSS spec and most software color pickers is yet another example of programmer convenience winning over human-friendly design.
Kindle Fire using silk
Also the design is slick.