Never mind how our flies look to us, it's an interesting exercise - not to mention good practice - to consider how our flies look to the fish. We can tie the neatest, sexiest pattern in the world, but if it doesn't look anything like food when viewed from below, there isn't really much point in making the effort.
I've never really put much stock in creating ultra life-like imitations for surface patterns. Some people can tie beautifully crafted detached body duns, anatomically correct, which really do look the business in the vice. I have reservations about their effectiveness though; do the fish really key into the exact silhouette of the emerger or dun before deciding whether or not to snaffle the offering? I doubt it. Items trapped on or in the surface film create breaks in the integrity of the mirror-like meniscus when viewed from below - for example a set of six insect legs from a dun sitting on the surface on its tippy toes, will form the appearance of several little dimples considerably more conspicuous than might be expected. Drop a fly into a pint pot of water and take a look from below and you'll see what I mean - the confusion created in the surface tension belies the diminutive nature of the culprit above.
Anything which re-creates this busy messiness stands a good chance of being taken by a feeding trout, providing it's about the right size and shape, and irrespective of exact colour and realism. Most of the world's most enduring surface patterns key into this impressionistic style and I'm convinced that, for example, a good old Adams will take a fish every day of the week where an exquisitely tied detached body dun will sometimes fail.
Take the underside view below of the snowshoe hare emerger tied in the previous post; it's prime triggers are basic - the curved abdomen which penetrates the surface film, and the slightly straggly nature of the thorax which gives a general impression of unfolding legs and wings. The fly as a whole may not outwardly look much like an emerging dun, but it gives off the right impression where it matters most - from the perspective of the fish. I'm positive that this is why the fly - and other no-hackle patterns like it - are so deadly.