If by rz you mean red zebra (metriclima/maylandia estherae), there are a couple of answers to your question.
In Lake Malawi, numerically m. estherae (blue morph) predominates. Males are bluish and females are orange. This 'wild type' red zebra is one one of the few mbuna species that are dimorphic from birth (with most other dimorphic mbuna species the males undergo a color transition as they mature while females retain the juvenile pattern. Male 'wild type' red zebras bear a resemblence to the cobalt blue zebra (m. callainos), though there are differences.
M. estherae (blue), definately male due to color:
M. estherae (red or orange morph) seems to predominate the hobby with both males and females being orangish. I'm assuming this is the type you have since they seem to be the most common type of red zebra in the hobby.
As the males of this type of red zebra mature they may become lighter in color, sometimes nearly pinkish, and their dorsal fins take on a blue hue (the dorsals of females remain orangish. This gender difference develops while the fish are still small (less than 3").
Matured male m. estherae with blue-hued dorsal:
Young female m. estherae with orange dorsal
Larger mouth-brooding female with orange dorsal
Maturing young males (note the blue hued dorsals)
Small juvie of undetermined gender
There's also an orange-blotched (OB) variety of m. estherae (orange with black blotches).
