  Globular cluster (GC) stars composed of pristine material (first-generation,
1G, stars) are not chemically homogeneous, as they exhibit extended sequences
in the "Chromosome Map" (ChM). Recent studies characterized 1G stars within the
center of 55 Galactic GCs, revealing metallicity variations. Despite this
progress, several unanswered questions persist, particularly concerning the
link between the 1G metallicity spread and factors such as the radial distance
from the cluster center or the host GC parameters. Additionally, it remains
unclear whether the extended 1G sequence phenomenon is exclusive to old
Galactic GCs with multiple populations. This work addresses these open issues,
examining 1G stars in different environments. First, we combine Hubble Space
Telescope (HST) and James Webb Space Telescope photometry of the GC 47 Tucanae
to study 1G stars at increasing distances from the cluster center. We find that
metal-rich 1G stars are more centrally concentrated than metal-poor ones,
suggesting a metallicity radial gradient. Additionally, the two groups of 1G
stars share similar kinematics. Since our analysis focuses on giant stars in
the cluster center and M dwarfs in external fields, we discuss the possibility
that the metallicity distribution depends on stellar mass. Subsequently, we
analyze HST multi-band photometry of two simple-population clusters, NGC 6791
and NGC 1783, revealing elongated sequences in the ChM associated with
metallicity variations. Finally, we investigate the 1G color distribution in 51
GCs, finding no connections with the host cluster parameters. These results
shed light on the complex nature of 1G stars, providing insights into the GC
formation environment.
