Ukrainian world No 25 she wrote.
"I have been warned about the negative impact but I did not - and still don't - consider it a 'black face'.
"I did not intend to caricature but to share my feelings about the current situation: we should all be treated as equal.
"I am so disappointed my message has been corrupted. I sincerely apologise to all the people I have offended."
Yastremska has won three WTA titles in her career and has a Grand Slam best run of a fourth round spot at Wimbledon last year.