I do hope you understand that I often have a hard time saying what I mean without saying what I really mean. Things I say are always put out in as honest a way as I know how. I don't want to cast aspersion on another's way of doing things but it is sometimes difficult to write something that does not appear to do just that.
When I was very young and not yet even owning a fly rod I had seen men fly fishing. The graceful overhead casting was what caught my eye and my imagination as well. Over all the years and the many thousands of miles I've logged looking to go fly fishing it has always been those loops sailing so perfectly through the air that made some casters stick to my minds canvas. That's what I was trying to convey, just that for me, in my time, where I grew up, it was the dry fly that you thought of when someone said 'fly fish'.
By my own admission I have been a streamer tier and fisher for a great number of years, however the foundation was laid with the art and knack of and for casting those little dries.
I am a self professed dry fly bigot, that's the way I like to fish, so that's the way I fish.
I fish my fly dead drift about 15% of the time, the rest of the time, I fish a very active presentation. I rarely change fly patterns, I do constantly change presentation until I figure out what works.
I won't say the way I fish works everywhere, my home river is primarily a caddis fly factory. The only time a caddis fly floats dead drift, is when it is indeed dead. Caddis flies want to spend as little time hanging around as possible, the fish seem to know that as well, so they tend to be pretty quick when they want to try to eat one.
If you stop and think about it, alot of things floats on the surface in a dead drift - twigs, leaves, cigarette butts, and some flies. The only things that move on the water (with the exception of some of our flies) are things that are alive.
So fishing a fly dead drift relies entirely on having the fly look good enough to eat. On the other hand, if I can present my fly with a passable presentation, regardless of how it looks, the fish are going to think it is something alive.
I very rarely fish a fly that really looks like anything specific, I want it to look a little bit like alot of things. Let the fish figure out what it is. But I want a fly that I can twitch, skate, swing, dapple, and fish fish dry or damp, all sometimes on the same cast.
To be honest, it took me a long time to realize that things move on the water. I can't count how many times I fished dead drift all day long without a strike, only to catch my first fish as I was walking to shore with my fly dangling in the water behind me. I finally realized, maybe there was more to fishing a dry fly than just a dead drift.
Again, it may just be a function of the waters I fish, your mileage may certainly vary.
I didn't see any hatches but there were some rises to light colored insects (coulda just been plant matter) on the water.
They may have been sipping spent mayfly adults (spinners). Most mayflies will oviposit directly on or just over the surface of riffle areas in a stream, and then fall spent onto the surface. Trout will line up and just sip them right out of the surface film.
Just a guess given your description of trout rising to light-colored insects, or maybe plant matter.
As I said previously, when we use the correct imitation, feeding behavior determines whether a dead drift or animation will work.
In very basic terms, think about what we are doing when we fly fish. We are presenting a fly, and hoping that the fly happens upon a fish that is willing to eat it. If the fish is selective to animation, an animated presentation of the correct type is what works. If the fish is selective to hatch that presents itself dead drift , an animated approach will fail. If the fish is not selective, either approach may work.
When added to size, shape, and color, "behavior" is the 4th leg of imitation. Dead drift or animation by itself is neither right or wrong. It needs to be judged on 2 criteria: (1) Are the fish selective, and (2) if they are selective, what is the behavior criteria that matches the selectivity criteria.
Note that when animation is needed, it must match the behavior of the food. All forms of animation do not work. Think of dry fly animation like animation of streamer fishing. Sometime short strips entice a fish, sometime a long slow strip, sometimes a strip and pause retrieve.
The English learned this a long time ago then the would fish a brace of flies on droppers and they would use an anchor fly to anchor the line in the water. When they lifted the rod tip, the flies closer to the angler would rise out of the water and hang by the droppers dapping on the water. This simulated the naturals that would dapping on the water and enticing strikes.
The only thing I'll add to what Silver said, if one presentation isn't working, try something else. That is really the essence of my point. I've personally given up trying to guess what's going to work, I try different presentations. sometimes on the same cast, and more often than not stumble across something that works. Granted it's not scientific.
Certainly if a blanket hatch is going on, that's what you want your fly to look like, the closer the better. On my home river, blanket hatches are the exception, they occur maybe only 5 - 10 % of the time. The rest of the time will have a variety of bugs on the water, none in overwhelming numbers. That's when I like to fish a generic looking pattern. MOre often than not in this type of situation, a good presentation (dead drift or active) with generic looking fly will work.