Welcome to the Community! Please don't EVER hesitate to ask any question you might have about your bird, there is no such thing as a "stupid" question!
At first I wasn't sure what you were asking about, but after reading Sailboat's response I now understand...I don't know much about Mynah's, but I do have extensive experience breeding and hand-raising parrots, so I've closely seen and handled hundreds of newly-hatched chicks.
I don't know what the growth progression/timing is for a Mynah Bird, as far as their "stages" of growth and the ages that correspond with those stages, but at only 50-days old (less than 2-months old) he's still an extremely young baby, and it's not at all unusual for a baby bird's skin to appear very pink/red...And as Sailboat already mentioned, birds have extremely thin and very translucent-looking skin at any age. So this is not unusual at all...
****HOWEVER, if it's ONLY THAT 1 LEG that appears to be red, or if ONLY THAT 1 LEG is that color of red, compared to the other one, then there might be an issue...However, we don't know anything at all about this baby Mynah Bird, such as:
-Is it being hand-raised by you, or is it being raised and fed by it's parents?
-Is it housed alone, or is it housed with other birds?
-What type of cage is it being housed in? Nest-box? Brooder? Is it possible for this baby to hurt himself on the cage material, or could it have fallen off of something, like a perch?
-DID YOU PUT A BAND ON THAT PARTICULAR LEG? If so, at what age did you band it?
What I'm getting-at here is that if that one leg is much different-looking than it's other leg, much more red in color, or if you see any signs of it having-been pecked-at or injured (any exterior wounds/bite-marks, any blood, any limping or favoring of that leg by the baby, etc.), or if you notice that this baby is showing any signs/symptoms of being sick or in-pain (is the bird very lethargic, sleeping a lot or not moving a lot, quiet, fluffed-up all the time, any constant crying sounds, any vomiting, runny droppings, etc.), then it's possible that he has hurt his leg or another baby or it's parent's have injured his leg, and it may be infected. If you can give us some more information and maybe a photo of it's other leg to compare it to, then we can better help you out...