  The color-magnitude (CM) diagram of cool dwarfs and brown dwarfs based on the
recent astrometry data is compared with the CM diagram transformed from the
theoretical evolutionary tracks via the unified cloudy models (UCMs) of L and T
dwarfs. A reasonable agreement between the models and observations is shown for
the whole regime of ultracool dwarfs covering L and T dwarfs, and this is
achieved, for the first time, with the use of a single grid of self-consistent
nongray model photospheres accommodating dust cloud (UCMs with T_eff between
700 and 2600 K). A distinct brightening at the J band in the early T dwarfs
revealed by the recent parallax measurements is explained as a natural
consequence of the migration of the thin dust cloud to the inner region of the
photosphere and should not necessarily be evidence for Burgasser et al.'s
proposition that the dust cloud breaks up in the L/T dwarf transition. Also,
the rapid bluing from the late L to the early T dwarfs is a direct result of
the transition of the thin dust cloud from the optically thin (tau < 1) to
thick (tau > 1) regimes while L_bol and T_eff} lower only slightly. Thus, the
theoretical evolutionary models, the cloudy models of the photospheres (UCMs),
and the observed fundamental stellar parameters aqre brought into a consistent
picture of the newly defined L and T dwarfs.
