I am afraid that functionality like adding a custom "wash" colour to change global settings of buttons or other attributes will not be implemented. Some of them are styled with image so it is not justified to make new sprite image by adding button="green" .
However, to achieve your goal you can use a custom skin. In our feature releases there will be a list with the new changes in the Skins and you could update only the necessary CSS rules.
I hope this helps.
All the best,
the Telerik team