  We carry out and analyze new multi-color photometry of the Galactic globular
cluster (GC) M75 in UBVI and focus on the brighter sequences of the color-
magnitude diagram (CMD), with particular emphasis on their location in U-based
CMD. Specifically, we study the level both of the horizontal (HB) and red giant
branches (RGB) relative to the main-sequence turnoff (TO) in the U magnitude.
Along with the presented photometry of M75, we use our collection of
photometric data on GCs belonging to the metal-poor range, [Fe/H]zw<-1.1 dex,
obtained from observations with different equipment, but calibrated by standard
stars situated in the observed cluster fields. We confirm our earlier finding,
and extend it to a larger magnitude range.We demonstrate that DeltaU_{TO}^{BHB}
expressing the difference in U magnitude between the TO point and the level of
the blue HB, near its red boundary, of the metal-poor GCs observed with the
EMMI camera of the NTT/ESO telescope is about 0.4-0.5 mag smaller as compared
to GCs observed with the 100" telescope and 1.3 m Warsaw telescope of the Las
Campanas Observatory. At the same time, Delta U_{TO}^{RGB}, the difference in U
magnitude between the TO and RGB inflection (brightest) points, does not show
such an apparent dependence on the characteristics of U filters used, but it
depends on cluster metallicity. We have shown, for the first time, the
dependence of the parameter DeltaU_{TO}^{RGB} on [Fe/H] and have estimated its
analytical expression, by assuming a linear relation between the parameter and
metallicity. Its slope, Delta U_{TO}^{RGB}/Delta [Fe/H]~1.2 mag/dex, is approx.
a factor of two steeper than that of the dependence of the RGB bump position in
the V magnitude on metallicity. The asymptotic giant branch (AGB) clump and
features of the RGB luminosity function (LF) of M75 are also discussed.
