The "Bad Boys" hitmaker, 31, won the show in 2008 but, speaking in a candid Instagram video, she revealed she was told she would have to work "10 times harder than a white artist" as she began recording her debut album.
Delving into the "microaggressions" she experienced from various music label executives throughout her career and how she has struggled, Alexandra explained she was even told to "smile more on Instagram because you come across as aggressive".
"The music industry is such a funny little place," she detailed. "I love singing, I love what I do but if it wasn't for the love that I have for music I definitely wouldn't be in this industry."
"A few reasons are, when I won the X Factor I was told, 'Right, because you are black, you are going to have to work ten times harder than a white artist, because of the colour of your skin... You can't have braids, you can't have an afro.' You can't have anything that basically is my identity: 'You have to have hair, for example, that appeals to white people so they can understand you better'."
She added: "That was so hard to digest. I was told to bleach my skin and that was something I refused to do."
The "Start Without You" star also opened up about the abuse she received from trolls when she competed on ballroom dancing TV show "Strictly Come Dancing" and injured herself, insisting: "How I got through it, now I look back and I have no idea, no idea.
"I don't even like thinking about that experience at all. But thankfully, my family and friends got me through it and the amazing fans that supported me."
She went on to urge fans to "speak your truth", adding: "That's all we've got. We have one life."