Updated Fade?

Hello- I would like to change the default colors of the “updated fade” effect which displays when a new post is saved on the admin-post page. On line 352 of the admin-post page, there is a reference to: “div id=”message” class=”updated fade.” I’m assuming/guessing that the “class” is a CSS reference, but I cannot find this reference in any of WP’s CSS files. Does anyone have an idea where the code for this effect might be so that I can try to make some edits?
Thanks!!!! DB~