The idea of alternating colors on the steps has been pushed by a number of different sources, but is also something of a horror to others. Those who advocate it usually have relied on "tests" with random groups of people, but the "randomness" has seldom been documented.

Different people react differently, and for some people the alternate colors are strongly "disorienting." The consensus of opinion from those actually involved in serious human factors and safety is that a uniform visual image with each individual step marked so that it's easily "targeted" is least likely to trigger disorientation in the largest possible number of potential users.

Each step should stand out as an individual and identifiable separate object, with good visual separation from adjacent like objects; but the objects should all be essentially the same to avoid triggering disorientation in susceptible persons.

If two visual objects are different, the brain has to make a choice between "objects of one kind" or "objects of another kind," in addition to chosing the specific object of the selected kind. Most people don't have a problem with it, but that's confusing to a few people. The choice of "which one of these all-the-same objects comes next" is less likely to cause a "brain fart" that can result in an accident for those who are susceptible.

A contrasting "nose" on each step is an essential feature. It has also been found helpful in some cases to have a side "edge" on each step with a contrasting color, often to match the nose, so that each individual step has a "U-shape" (with the nose) in visual pattern. Carpeted stairs ideally should never be carpeted in flat tones to the edge, since the "bare stair" at the edge helps to make each step an identifiable "image" easily separated from the mass of steps. A contrasting carpet side stripe can serve for this aid to "step separation" if you really want to have carpet all the way across. "Stair carpeting" is available in standard widths that incorporates the needed stripe along the sides, if you choose full tread carpeting.

Good lighting is, of course essential.

You can find lots of arguments for and against the alternate color thing. Most of what I find "for" it is more opinionating than tested/testable information. If you can make it "pretty," then go for it; but there are adequate and safe design features that can be used that are as good or better from the safety aspect.

It's an idea like the mandatory "child proof" caps on prescription medicines. If you can't get the lid off you may die, but the kids are safe. A safety feature has to consider all those who may use it, and the alternate colors may help some, but are suspected of decreasing safety for some people, at least by some credible sources.

John