Q: Do the RR Lyrae stars cover a wide range of apparent magnitudes,
or do they all have roughly the same apparent magnitude?
The colored symbols are grouped together
in a region roughly
14.5 <= apparent mag <= 15.0
which is a pretty narrow range.
Q: What does that imply about the range of ABSOLUTE magnitudes
for these RR Lyrae stars?
Since all these stars are at the same distance
from us, the absolute magnitudes are equal to
the apparent magnitudes plus some constant offset
called the "distance modulus":
(m - M) = distance modulus
The distance modulus is related to the distance like so:
(m - M) = 5 * log(d) - 5
The fact that the apparent magnitudes have a narrow range
means that the ABSOLUTE magnitudes also fall within
a narrow range.