How to change the [url] tag link color?

[Velocd]

The link color used by the [url] tag does not match my style postbit backgrounds, therefore I need to change the default [url] link color somehow. I'm referring to the [url] tag that members use in their posts. I would like to instead use a stylesheet custom link color I made, so I need to find the code being replaced by the [url] tag, so I can insert class="grey" at the end of the <a href="">. Thus everytime someone uses [url] tag, their link will be using my class="grey" attribute, to obtain that color.

Also when somebody simply types a url in, since it auto-parses it to url format, I need that to be of my class="grey" color.

How can I do these two things? Any help would be great.