A great feature of flat keyboard restaurant style cash registers is your abilty to create new keyboards as well as update existing one. We simply use word templates and they allow you to change the color of each button, the text and a picture if you wanted. A good cash register company will provide you with the template so you can print your own on demand or make changes as needed.
Here are a few links to some pre-made keyboard templates and keep in mind many cash registers use the same template. Also little word of advice please print a blank, cut it to size and make sure it fits before you spend a few hours building a custom template only to have it not fit.