  Recently, near-ambient superconductivity has been experimentally evidenced in
a nitrogen-doped lutetium hydride by Dasenbrock-Gammon \emph{et al.} [Nature
615, 244 (2023)], which yields a remarkable maximum $T_c$ of 294 K at just 10
kbar. However, due to the difficulty of x-ray diffraction (XRD) in identifying
light elements such as hydrogen and nitrogen, the crystal structure of the
superconductor remains elusive, in particular for the actual stoichiometry of
hydrogen and nitrogen and their atomistic positions. This holds even for its
parent structure. Here, we set out to address this issue by performing a
thorough density functional theory study on the structural, electronic,
dynamical, and optical properties of lutetium hydrides. Through thermal and
lattice dynamic analysis as well as XRD and superconductor color comparisons,
we unambiguously clarified that the parent structures are a mixture of dominant
LuH$_2$ phase of the CaF$_2$-type (instead of originally proposed LuH$_3$
structure of $Fm\bar{3}m$ space group) and minor LuH phase of the NaCl-type.
