Googling around is inconclusive as to which is correct, if not both. If I am describing someone hair, is it “bleach blond hair” or “bleached blond hair”? (Is there a definitive answer for this?)
I would say a person can be a “bleach blond” or a “bottle blond”, but hair is bleached blond.
For “bleach blond hair” are you referring to the hair that is on the “bleach blond”?
Bleached blond hair sounds kind of like hot water heater to me.
ETA: Both bleach and blond are words that start looking very odd when you’ve read them a few times.
Bleached blond.
It’s blond because it was bleached. “Bleached” is thus a past participle functioning as an adjective. “Bleach blond” doesn’t really make sense grammatically, but it’s human nature to say things as briefly as feasible, so the “-ed” tends to get clipped, and when spoken it will often sound like “bleach blond” even if the speaker is thinking “bleached blond.” Many people will hear that uncritically and repeat it as well as write it that way.
Black roots hair. 
Be that as it may, the colloquialism is “bleach blond”.
Bleach blonde.
Anyway, one of the problems with “bleached blond” is – try saying it out loud. The tongue and lips get all tripped up. “Bleach-da blon-da.” It’s just plain harder to say.
(I first encountered this effect playing D&D and fighting a “demon hound.” Try saying it out loud, and your mouth will start forming it as “demond hound.”)
I’ve only heard bleached blonde. The other one does sound odd to me, because the person is only blonde because the hair was bleached.
Perhaps if I’d often heard the other it wouldn’t sound so odd to me.
Saying “bleach blond” is the equivalent of saying “smoke barbecue” or “pickle beets”. It’s just plain wrong, no matter what you might hear colloquially. Writing things the way they are colloquially heard does not make the writing correct.
How does is sound when compared to, say, “peroxide blonde?”
I went to 10th grade in Honolulu, Hawaii, where my 10th grade English teacher had some words for us students on-topic similar to this.
Snow-cones are massively popular there, but they aren’t called snow-cones (ETA: because, I think, Sno-Cone is a trade-marked name). They are called “shaved ice”, but commonly just “shave ice”. This English teacher felt it quite important for us to know that it was “shaved ice” (i.e., ice that has been shaved).
It’s relevant to note at this point, that this teacher was a Chinese person (although apparently at least a long-time American, if not second-or-more generation, since she spoke thoroughly fluent English). She also insisted that a certain popular Chinese-American item of cuisine was properly called “chopped sui” (i.e., sui that has been chopped), and not “chop sui”.
Um… Negatory on that. Chop sui isn’t sui that has been chopped. It’s a Chinese name. (Actually, to the best of my knowledge, it’s a pseudo-Chinese dish invented in America and given a pseudo-Chinese-looking name.) So it’s “chop sui” because that looks Chinese and that’s the name that was given to it, however that happened. It’s still not sui that has been chopped.
Huh. I always knew it as chop suey.
When I lived in Hawaii, I was often tempted to confuse it with char siu, though.
Grammatical correctness has nothing to do with how the English language is spoken . . . or written, for that matter. I’ve heard “bleach blond” all my life, and never “bleached blond,” no matter how grammatically correct.
As it is entirely a bit of slang, how it is colloquially said is what is correct. And if you need precedent, we refer to people as being “teenage,” not “teenaged.”
Okay, now that you mention it, I guess “chop suey” is the right spelling. The Wikipedia page has an extensive section on the many myths of the origin of this dish; but it looks like maybe it actually did originate in China after all.
It still isn’t “chopped suey”, and it isn’t suey that has been chopped.
Oooh, I have a question to add to this discussion. I grew up drinking “ice tea”, but I suppose it was really “iced tea” and I misheard it. Which one should it be?
“We got the bubble-headed bleach-blond, comes on at five,” courtesy of Don Henley. And if you can’t believe Don, who can you believe?
But from Michael Hutchence of INXS we have Suicide Blonde
What’s that have to do with “bleach blond” vs “bleached blond”? 
My experience was just the opposite. Having been raised by a literate family who endeavored to use correct English, I just assumed when I heard the phrase, that people were saying “bleached blond” because I knew that that would be the correct form. So my ear heard what my mind expected it to hear, and “bleached blond” was what I heard, but often with the /-ed/ elided in vernacular and colloquial conversation. Even if it sounded like “bleach blond”, I would have written “bleached blond”.
Please allow me to draw your attention to what Ngram Viewer has to say about this:
An overwhelming majority of professionally-edited writers, by maybe a 10:1 margin, spell it “bleached blond”.
A bottle blonde gets his/her blondness from a bottle.
A peroxide blonde gets his/her blondness from peroxide.
A bleach blonde gets his/her blondness from bleach.
In “bleached blonde”, “blonde” is the important word, “bleached” is a modifier. “Bleach blonde” can operate as a unit unto itself. One could even argue that “bleach” is the more important word, with “blonde” as sort of a modifier.
It is a subjective judgement, and the “correct” choice depends entirely on context.