Our 2005 350L is our third Hyundai.  With regard to the heater/air
conditioner "lights", indeed they are just about impossible to read in
sunny weather.  The trip computer and clock are slightly (but not
much) better.  The numbers and letters are there, though.  I would
have to assume it was a design fault as against anything specific with
your (and our) car.  :-(

As a footnote, our 2005 Sonata GLS-SV center console lights are
brighter, but still leave a bit to be desired on a bright day.

Our 2000 Sonata GLS did not have the automatic temperature system, so
the only center console "lights" was the clock which was bright and
easy to see in any level of brightness.
Kent