  The recent report of near-ambient superconductivity in nitrogen doped
lutetium hydride has triggered a worldwide fanaticism and raised major
questions about the latest claims. An intriguing phenomenon of color changes in
pressurized samples from blue to pink to red was observed and correlated with
the claimed superconducting transition, but the origin and underlying physics
of these color changes have yet to be elucidated. Here we report synthesis and
characterization of high-purity nitrogen doped lutetium hydride
LuH$_{2\pm\text{x}}$N$_y$ with the same structure and composition as in the
main phase of near-ambient superconductor1. We find a new purple phase of
LuH$_{2\pm\text{x}}$N$_y$ between blue and pink phase, and reveal that the
sample color changes likely stem from pressure-driven redistribution of
nitrogen and its interaction with the LuH$_2$ framework. No superconducting
transition is found in all blue, purple, pink and red phases at temperatures
1.8-300 K and pressures 0-30 GPa. Instead, we identify a notable
temperature-induced resistance anomaly of structural and/or electronic origin
in LuH$_{2\pm\text{x}}$N$_y$, which is most pronounced in the pink phase and
may have been erroneously interpreted as a sign of superconducting transition.
This work establishes key benchmarks for nitrogen doped lutetium hydrides,
allowing an in-depth understanding of the novel pressure-induced phase changes.

Superconductivity;Materials Science