Once you go black, you never go back?

This sentence isVulgar/Sexy SlangOriginating from American popular culture (spreading from hip-hop/movies/talk shows in the 90s or earlier), its core meaning is:

OnceBlack person(Usually referring to Black men) After having sex, they feel "it was so good" or are super addicted to "size/skill/stamina/feeling", and feel "I can't go back" when they have sex with other races (especially white people) and are completely unsatisfied.

Simply put, it glorifies/stereotypes Black men as being "especially strong" or "especially big" in bed, so that "once you try it, you'll be addicted and never look back."

Other possible puns or humorous uses

Dyeing hair black: Once you dye your hair black, you never want to go back to light color (because black hair makes you look slimmer/better).
Eat things like dark chocolate, black sesame seeds, and brown sugar: Once you try dark-colored sweets, you'll fall in love with them.
However, in the case of 99%, especially in sexually related conversations, everyone knows it refers to...interracial sex(Interracial sex), especially the stereotype of white women and black men.

How do we view this in reality?

This statement is essentiallyRacial stereotypes + sexual fantasiesThe product of this is something that many Black people themselves find funny or uncomfortable (because it reduces people to "size" or "performance").
In reality, everyone has different preferences, and size/skill has no absolute relation to race. Orgasm is more related to emotional connection, foreplay, and communication.

The most classic & most common variations

Once you go black, you never go back
The original version, targeting Black people (usually Black men and White/Asian women), emphasized that "Black skin feels amazing" or that their "size/strength" was so great that once you've tried it, you can never go back to other races. In Hong Kong/Chinese-speaking regions, it was directly translated as "Once you've tried Black people, you can never go back."

Once you go Asian, you never go Caucasian
(Once you've tried Asians, you'll never want to try Caucasians again.)
This is a common stereotype among white/black communities regarding Asians (especially Asian women), emphasizing "refined skills," "obedience," "endurance," or "small but powerful." Someone on Reddit said that after their ex-boyfriend was Korean, they "never go Caucasian."

Once you go white, you know what's right / Once you go white, your credit's right
(Once you've tried it, you'll know what's right/what's trustworthy.)
The humorous version targets white people (usually white men), playing on double entendres of "white people have good credit," "are rich," "have stability," or "legal rights." It's commonly used in stand-up comedy for interracial couples for self-deprecation or retort.

Once you go Latino / Latina, you never go back
(Once you've tried Latinos, there's no going back)
It emphasizes that Latins are "passionate," "hot," "rhythmic," and have "dance-like sex."

Once you go brown, you never go down
(Once you've tried brown, you won't go any lower/downward)
A variant of Indian/South Asian/Latin brown skin tone, this is how Indian men boast.

Once you go ginger, you never go back
(Once you've tried red hair, there's no going back.)
They used "hot" and "unique" references to target red-haired white people.