^Agreed.
For understanding purposes, you can take it this way.
OOOO OOOO
OOOOOO OOOOOO
OOOOOOO OOOOOOO
OOOOOOOOOOOOOOOOOOOOOOOOOO
OOOOOOOOOOOOOOOOOOOOOOOOOO
OOOOOOOOOOOOOOOOOOOOOOOOOO
OOOOOOO OOOOOOO
OOOOOO OOOOOO
OOOO OOOO
Imagine the above is an RBC and O represents the haemoglobin molecules. Since haemoglobin gives the pink coloration to a RBC, and its present in larger amounts on the outer side, the outer side looks more reddish than the inner side, which is flattened.