Why another colorpicker module?

That's the farbastic colorpicker. This one is the jqeury colorpicker. Honestly, beyond that there isn't a significant difference.

Basically it's a matter of preference as to which you like, as they essentially do the same thing - allow you to create a form element that has a color picker attached. This one is laid out more like the photoshop color picker, so for designers they will find it more native to what they are used to, but they will find the farbtastic module just as easy to use I'm sure. The farbtastic module also displays the hexadecimal color code to the user, while this one takes care of all that in the background. Personally, I prefer the look of the jquery colorpicker, but that's entirely a personal preference, and I have no doubt that other people will prefer the look of the farbtastic color picker.

@Boobaa as Jay noted the difference is the JavaScript powering the color picker. Having more than one choice is a good thing.

Maybe if both projects could link to each other on their project pages, to help people discover the two possibilities?

here's an idea

merge with colorpicker module and support both scripts, the Fartbastic Colorpicker and the jQuery Colorpicker.

there are some modules that act like APIs that support multiple libraries.
naming a few: Starbox API, Charts, WYSIWYG, Views Slideshow (attempting to support multiple types of slideshows).

having a common API, there would be no need for duplication and the CCK module would apply to both scripts ;)

I'll be honest, the idea potentially has merit, but there are also some pitfalls that make me not want to do it.

Let's look at the Wysiwyg module. It works quite well - but really, what is the point? I've never seen a site that had the need for more than one Wysiwyg editor on the site. I actually used the Wysiwyg module on a site, but it just seemed to me to be adding unnecessary bloat. I also found that some features were lost with some editors, as the API was made to deal with any editor in a general fashion.

Now I just use the module for the specific editor that I want to use (CKeditor in my case).

Bringing that idea to the color picker modules, it would require turning the module into two things:

1) an API module
2) the module for the specific colorpicker that the user wants to use

Right now, these features are served fine through one module (or at least such is the case with the jquery colorpicker). Moving it into an API would require having two modules, and potentially losing funcitonality from the jquery colorpicker module as a result. And I really don't see anyone having the need for more than one colorpicker module on their site.

The primary advantage that I see is as you mentioned CCK support. This would be great, but I'd actually just prefer to get CCK support for this module. I've been advertising for a co-maintainer to work on this, hopefully one will come around soon.