Colin Kaepernick is mourning the death of Harry Belafonte ... paying tribute to the legendary singer and civil rights activist by thanking him for his mentorship and leadership.
The former NFL quarterback took to Instagram after news of the "Day-O" singer's passing broke on Tuesday ... sharing a photo of them together with a sweet note.
"Thank you, Mr. B, for all of your years of mentorship, guidance, and lifetime of activism fighting for a better future for all of us," Kaepernick wrote.
"You will be missed by many, but your memory and impact lives on.