If you all ever want a true education on dry fly fishing, look no further than Gary LaFonataine's book "The Dry Fly".  Talk about a boatload of info, and definitely not the same old stuff.  As per the way he usually investigates things, many hours spent underwater in scuba gear were part of the process, watching people fish different flies & techniques and the trout responses.

For Attractors, dries that are meant for searching the water during non-hatch periods, he has a chapter entitled "A Theory of Attraction", and it basically tells you what color fly to fish under various light conditions/backround colors.  Pretty much takes the guesswork out of picking the color, except for certain flies like the Royal Wullf & Trude, which are good under any light conditions (except cloudy days).  He came up with a specific design called the Double Wing that maximizes the impact of color.  Here is a quick summary of some of the basic colors & when to use them:

1. White- shade, dusk, or anytime on a brown trout stream (they like shadows)
2. Gray- cloudy days
3. Orange- sunrise, sunsent, and during the Autumn
4. Lime- midday, or anytime on heavily wooded streams when the leaves are green
5. Royal- all around attractor, anytime the sun is out, but not so good on cloudy days
6. Black- at night
7. Yellow- mid-morning, mid-afternoon, during rain storms, and when a lot of yellow bodied    insects are around
8. Pink- early morning & late afternoon

The theme is matching the color of the fly to the dominant color of the ambient light.  When light hits an object, we perceive it's color due to light bouncing off the object- if an object is orange, then it absorbs other wavelengths and bounces the orange light back to our eye, creating the color.  By matching the fly to the ambient light, it stands out & appears bright or as LaFonataine likes to say "On fire".

This book has so much info in it that my head hurts if I spend more than a little while reading it.  It truly is a wealth of info, and it is different stuff than you will see anywhere else.  It's a shame he died  of ALS, he still had so much he wanted to investigate & write about.  I bet he would have done an amazing book on nymphs eventually, he wanted to do one on streamers & another on bass. 

I can already see validity to some of the fly color stuff- for example the deadliness of a White Wullf on the Housatonic, esp. in the evening.  And I've known guys who swore by a bright orange spinner in the evenings.   

Juice, you're really getting to know Torrey well, aren't you? 

I've heard Borger (the one that doesn't ride on coattails) say the same thing about using bright orange spinners when the fish are keying on them as the sun is going down, during that time of day when the sunlight is that bright orange. I can't remember exactly if he said bright orange body, or maybe it was wings, but the theory was the same about the sunlight absorption interaction with the fly.

Juice-

Gary who??  Dunno who you are talking about.

Yeah, Gary is a CT boy originally, he logged well over 1,000+ days on the Farmington, as well as a bunch on the Housy too. 

In keeping with Gary's theory of attraction, I've had great luck in the evenings with a Usual dubbed on fire orange thread- the body glows orange when it's wet.

Thanks for this post! Being a small stream brookie angler, attractors are a huge majority of what I fish with. 

In keeping with Gary's theory of attraction, I've had great luck in the evenings with a Usual dubbed on fire orange thread- the body glows orange when it's wet.

That's amazing, the other day, Sunday to be exact I fished the crap out of an orange sulfur pattern and didn't get so much as a strike. It was a lousy night I'd say for both sulfurs and the iso's. not many rises and there where alot of other bugs on the water....Caught one fish on tan caddis that is all.

In keeping with the color theory...Black.  When the sun goes behind the hills and fish are still coming up I like to tie on a Black bivisible type of fly.  Its basically black hackle palmered up the body over black thread.  In small sizes(18-24) I tie on a little tuft of muskrat fur about a third of the body length of the fly off the tail.  It really hammers fish from dusk through dark.  I have used this on the Farmington, Housatonic, Deerfield, and various Colorado streams.  Its very easy to see if there is alot of glare on the water too...which there often is at this time of day.  Super simple and works on both caddis and mayfly hatches. 
Also, back when I hit the beaches for stripers after work a few years back, we always used black or purple flys at night. Doesnt matter what type of bait that was prevalent, we always made sure to have something be it a clouser deciever or puglisi fly or in some cases plugs in black and or black/purple. During bright sunny days white or yellow flies or plugs were the ticket. After 20 years of surf/jetty/boat fishing for stripers you could really narrow it down to black, white, yellow and chartruese if all else failed.