two questions for the simplest slides

["Pablo Rodríguez" <oinos@web.de>]

Hi there,

I would like to create the simplest slides ever. I have done in LaTeX
before, but I'm not sure how to do it with ConTeXt.

All I want is to be able to center both vertically and horizontally
whatever each slide contains and to change background and text colors in
an easy manner (something like from now on background is red and text is
white).

Looking to http://tug.org/pracjourn/2006-2/schmitz/ and
http://wiki.contextgarden.net/Presentations, I still have two questions.

How can I get every single slide, no matter there is text or images,
vertically centered?

How can I change background and text colors after a \page? I mean
something like:

\setuppapersize[S6][S6]
\setupcolors[state=start]
\setuppagenumber[state=stop]
\setupbackgrounds[page][background=color,backgroundcolor=red]
\startcolor[white]
\starttext
Page is red and text is white.
\page
Page is blue and text is yellow.
\page
Page is green and text is white.
\page
Page is white and text is black.
\page
Page is red and text is white (again).
\stoptext

I mean, I know how to start, but I don't know how to change after the
start. And it would be extremely helpful to change text colors with a
switch (if that were possible), not within an environment (mainly
because most slides will only contain one of two words).

Many thanks for your help,


Pablo
-- 
http://www.ousia.tk
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