So maybeeee there should be universal support for this in WordPress. I feel like some of these features are common sense for smart platforms. Here goes anyway...
CustomPress is fabulous. Absolutely fantastic. I did notice that 20px icons fit perfectly. Thanks for that.
Request: Colorize the whole button.
Many of my clients or friends who I build sites for have very little, if-any experience. Some of them are a little older, and/or are very busy. Remembering what every item on the menu does is nearly impossible. They aren't really web-people. They're people-people. They run non-profit organizations or big business and don't have a lot of space left in their head to figure things out. So if I could tell my clients "go to the backend, click the Red Button on the menu on the left"... they are more likely to retain everything. This would also help for those of us who want to build customized documentation for our clients or visitors who need access to the backend various purposes.
Now I know there are a number of plugins that let you manipulate the CSS of the backend and there are a handful of Admin themes in places like Themeforest/Codecanyon that might do this. Seems to me like the perfect place for a feature like this would be CustomPress.