Android : How To Change Size / Color Of Phone Buttons?

I would like to know the way to make a user interface for Android for people that have low vision. The idea is to make a UI with the following features: 1- Uses very very big buttons. 2 -Uses very big font size. 3- Te colors to use are basically black and white (for more contrast). 4- The icons in this UI are not relevant. 5- We must sacrifice the number of chars that we can show in the screen to get bigger labels and buttons. 6- A simple zoom system for the images should be a great idea. 7- We can use the camera of the phone to get a magnifying glass. I'm member of a blind people association in Spain and we think that this should be a great idea for begining a new low-vision-user- interface that is not aviable in the market for the new mobile phones. This will help many people that uses movile phones but have many difficulties to work with them.