color: move 'write' logic to the core ui class
One more step, the support for writing color is not directly in core. No
behavior change for the default case ('_colormode' = None).
Here are the details of what we have to change to the core method:
* apply to 'self.label' to input in the buffered case
* dispatch to 'win32print' when applicable
* apply to 'self.label' to input when applicable
http://example.com/no/anchor, branches: (None, [])
http://example.com/an/anchor, branches: ('foo', [])
http://example.com/no/anchor/branches, branches: (None, ['foo'])
http://example.com/an/anchor/branches, branches: ('bar', ['foo'])
http://example.com/an/anchor/branches-None, branches: ('foo', [])
http://example.com/, branches: (None, [])
http://example.com/, branches: (None, [])
http://example.com/, branches: ('foo', [])