The explanation in the dictionary of an "aim" is
The aim of something that you do is the purpose for which you do it or the result that it is intended to achieve.
and the explanation of a "purpose" is
The purpose of something is the reason for which it is made or done.
So are there any differences between "aim" and "purpose"?
And which word should I fill in the blank? "But for the _____of communication, we dress in clothes of different colors."