I have a poison eye for shades. Some blue hues look wrong. Some brown hues look downright nasty. I can't do pastels, but I like them on other people if it suits their skin tone.
Some colours that make my heart sink in the shops are:

- Pastels

- Neons

- The aforementioned soul sucking beige.

- Denim. Purely because it's so ubiquitous and boring.

Black and white look terrible on me, but can look great on other people.

Certain shades of orange and yellow suit me, but wearing them leaves me cold.

Pink. My mother used to try to dress me in pink but I stamped my little feet and said no. Still stamping...

Like Krish, I think mint is on my poison-eye list. I rarely even like it on others, silly though that is. Same with other sugary pastels. I don't mind colors that look like faded saturated colors, but don't like most pastels. It doesn't make sense.

But then there's neons which look horrid on me, bring back bad flashbacks and yet still call my name. I even bought a couple of neon necklaces to try the flashback trend. I make no sense.

No poison eye for any color here. The closest might be bright Barbie pink.
I had an aunt that hated pink and blue together. When I see it I can't help but think of her.

Burgundy. With my red hair it's a train wreck. And the olive tweed jacket and forest green jeans DH insists on wearing together. He thinks they match because they are both green. Ouch my poor eyes.

No poison eye for any colour here. I love 'em all - but I don't love them all equally and I certainly don't love them all on me. But that's a different thing.

I will say that lots of pastels worn together (or even displayed together, in stores) tend to make me turn away (perhaps partly because I don't look good in true pastels). Ditto a whole lot of neon at once (thought I like a shot of it now and then).
I have a poison eye for any color that reminds me of poop or puke. While house hunting a few years ago, I saw a dining room that was painted a sickening brown color that reminded me of you know what. I couldn't stand it, and wondered what kind of person would put an unappetizing color like that in a dining room. Just saying!

Beyond that, there are colors I don't wear because they don't look good on me; but I like those colors on the people who can wear them.
Funny, I was just thinking about this the other day. I love most colors, but am very picky about pinks and greens.
Pinks - I like blush, coral pinks, and fuschia, but hate Pepto/Barbie pinks.
Greens - I like emerald, lime, turquoise, teal, olive, and kelly green - hate muddy sage, yellow-greens and for some unknown reason I have a real problem with hunter green.
And there's a shade of brownish orange that is just awful.
I think I'd have to say that pastels are tough for me with the exception of certain blues and grayish lavender colors. I don't care for pastel yellow, pink, coral or green esp. They make me think of baby room colors.
I don't like most oranges and some yellowy greens but for the most part I like most colors. I can't wear yellow at all but I really like the color on others. Soul sucking beige looks awful on me so I avoid it but I don't dislike the color. I don't like to wear most pastels because they feel too twee (but I'm trying to get over that this season since pastels are so trendy right now) although pastel pink looks GREAT on me. I have a maternity sweater that someone gave me in pastel pink and it makes my skin look fabulous, but even that doesn't make me love it.
Hi five Joy and Suz for not having a poison eye for colours either :). I CANNOT be a successful fashion stylist and have poison eye. I try very hard to limit my poison eye for things. I am down to four and half things now, and I really want to keep it that way. If I could make those 4 and half things disappear - I would!

Gaylene, I've seen people pull off that yellowy-brown "phoo colour" to perfection actually. In Africa in particular. It is a stunning colour on a very dark skin tone.

Denise, so with you that tan when worn with white looks better on most people than black.

It's a tall order, Debs! Black from head to toe is extremely hard to pull off to my eye. Anna did it last week and I loved her outfit. She also looks good in black, which few people do. You are challenged :). But in the same breath I must add that your style needn't please my style eye - it has to please YOUR style eye. That's always the most important thing. You have to wear your outfit, and not me :).
No poison eye for color in general, but I do have colors that I don't like ON ME. Besides those that just don't flatter (SSB, muddy pastels, mustard), I don't really like to wear bubblegum pink, coral, periwinkle, dark purple... I guess they feel too feminine or something.

I also definitely dislike certain color combos - black and red, primary red and primary yellow (the ketchup and mustard effect), Superman red and blue, and 80s brights with black (really feel the need for a soft neutral to tone those down).
The only color I really don't like is the deep pink/red hue in a shade of purple- it makes my skin look the same shade! UGH