AdminXML Plus [0.3]

[Tyblitz]

So it only allow us to change colours of original admin theme, am I right?

That means the 9 colors you can customize in admin.xml. I believe the GetSimple design is balanced and there's a reason only those are customizable by default. The aim of this plugin is not to provide more  customization options, but to facilitate existing ones & to lower the barrier for creating community admin themes. 
I might be adding a couple non-themeable ones (like text color, pagenav link inactive & hover, which are set resp. to black, lightgray & white), and eventually the possibility to replace the text logo on the left with an image, but that depends on demand for it.