There is factual evidence (some examples below) that Iguanas can have a reaction to colours and scents, for example articles of clothing worn by handlers and also aftershaves and perfumes, sometimes with dramatic reactions!
There have been many entries on forums to this effect, but it wasn't until Bob Ferrari a Californian Iguana keeper, brought to my attention that perhaps there should be a web page on the subject, that I decided to take up his suggestion.

Below are some examples people have reported to me on this subject.

First from Bob himself
Going back over almost two years, we used to have posts and discussion on Iguana owners getting bitten wearing a particular color like a loud RED, BLUE, YELLOW & DENIM, as examples of some of them.
My personal experience may interest you. My Iguana will be three in July. Every day of her life with me, I wear a white T shirt. She has accepted my wife as the Alpha and has bonded with her. Of course this annoys me because she is "my" pet. I had her spayed in January. Since that time, she became "wildly aggressive" with me, not my wife. She was darting at my face, my hand when trying to remove her food dish or feed her, and constantly puffing up.
After conversing with other Iguana owners that had spayed females and what solutions they ended up with. It was unanimous that WHITE was objectionable!. I decided to test this theory.
Very recently, twice, while displaying this aggressive behavior, I put on a light brown earthly flannel long sleeve shirt. She settled down, I could pet her, and feed her and "no" puffing up.
From a reliable source with years of experience, this finding was accurate. The Iguanas are most comfortable around earthly colors like GREENS, LIGHT BLUES, BEIGES, TANS, BROWNS, etc, etc.
When you hear of Iguanas during breeding season with gaping mouths charging their owners or for no reason during a non breeding time of year, bite their owner, then colours should be considered as a possible cause.

From Rachel in the UK.
Both 'Ig' and 'Bob' are petrified of me when I wear my "Royal blue" summer dress with white flowery bits!!! I think it's the whole dress thing with spots, because we both wear a lot of blue and it doesn't usually effect them like this, but the blue dress shows immediately that they are petrified and will do anything and everything in their power to get away from me,  I tried talking to them and stuff, but they wouldn't have it - their mom had been eaten by the big blue and white spotted monster, and it was going to eat them next!!!
However if I wear anything yellow, then they try and eat me!!!

One from Bob in America on fragrances.
Another issue is fragrances. There have been many past posts going waaaay back about Iguanas biting women's hair tracing it to fruit fragrance shampoo. One of our members has two juvenile Iguanas and one absolutely freaks out when she uses COCONUT hand lotion. The emphasis is on the Iguana owner thinking, "am I wearing something to cause this odd behaviour".

It seems that loud bright colours like whites, yellows, reds, light blues etc when worn as a shirt, dress, sweater or top of some kind can spook some Iguanas into this weird behaviour, same goes for certain fragrances, the obvious ones to get a reaction would be fruit scents!
A recent post on a forum told of an Iguana climbing a wardrobe to get at a strawberry scented gel candle which it then proceeded to eat! It could well be that earthy colours as seen by wild Iguanas daily in the rain forest habitats, are normal and non alarming, whereas they have no experience of large bright colours in their natural habitat and are genetically wary of these.

So the next time you go to give Iggie a handful of leaves and he takes off like Billie Whiz!...think for a moment, are you wearing something different he hasn't seen you in before? is it a bright colour? or are you wearing that "special offer" fragrance that you got last xmas.