Spacemist
Spacemist is the term for the ethereal substance that fills most of dreamspace, the expanse of space between the rews of Charos. It is also sometimes called "dreammist", and often referred to in the plural, as "spacemists" or "dreammists". Despite the name, it is not actually a mist or vapor, but closer to a gas, though technically it composes a separate state of matter unique to the esture of Ses. Spacemist is brightly colored and is transparent over short distances, though visibility in the spacemist is limited to about two to four meters in most of dreamspace, and even where the mists are thinner it never extends beyond three or four kilometers.
While spacemist is often said to have on average about five times the viscosity of air at normal atmospheric pressure, strictly speaking this isn't true. Rather, the spacemist exerts an apergetic force on solid matter that partially counters its gravitational acceleration; the result is that solid objects fall more slowly through spacemist than through air, to a similar extent as if it had five times the viscosity, but the actual viscosity of the mist itself as measured by other means is quite low. The mist does not have the same effect on liquids, or at least not to the same degree, which means among other things that the spacefalls plumment through dreamspace faster than solid objects. Sesi physicists still debate whether there is any relation between the apergetic force exerted by the dreammist and the gravitational countering effect of the antite in the interior of the rews; while there seems to be some similarity in that both oppose gravity to some extent, nobody has proven any causal connection.
Although inhabitants of Charos who live out their lives on the surface or within the interior of a rew may never come into contact with spacemist, given the vast expanses of dreamspace between the rews spacemist makes up the great majority of matter in the plane.
Composition
Like most matter in Ses, spacemist is made up of wavelets traveling more or less perpendicularly to the three-dimensional space of everyday experience. It is made exclusively of wavelets of the fundamental colors, uncombined into larger composites. What differentiates spacemist from other matter, on the microscopic scale, is that the wavelets of a given color in the spacemist are coherent and in phase. Because of this, they exert an additional force on each other aside from the better known sympathetic and metric forces: the gyrant force, which acts orthogonal to both these forces, effectively giving nearby wavelets a tendency to "orbit" each other. Because of this, the motion of the wavelets in the spacemist is qualitatively different from that of those in other materials; this is the cause of the spacemist's exility, and is also believed to be responsible in some way for its apergetic properties, though the exact mechanisms behind this are unknown.
The gyrant force also seems to play some role in maintaining the coherence of the wavelets of the spacemist, keeping it in this state of matter. It is possible for spacemist to transmute into other forms of matter, as for instance the spacemist near populated rews turning into air. In fact, spacemist brought into the atmosphere of a rew generally changes very quickly into air; it is not possible under normal circumstances to convey spacemist unaltered to the surface of a populated rew, though there may be extraordinary magical or technological measures by which it is achievable. It is generally theorized that the presence of conscious life on the rews in some way brings about this change, though, again, the details are unclear. Presumably the reverse process also happens, and air and other gaseous, liquid, or solid matter far enough removed from the rews dissolves over time into spacemist, but if so this is a very slow process, and has never been directly observed.
Color
The most obvious variation in spacemist is in the color—not in the chemical sense of the elementary colors that make up Sesi matter, but in the ordinary optical sense. Spacemist comes in all colors of the spectrum, from bright red through vivid yellow and green to blue and violet. Its color is always highly saturated; spacemist never comes in shades of gray or brown. The difference in color apparently comes not from a difference in chemical composition, but in a slight difference in density that affects its interaction with light. The color of the spacemist seems to have little discernable effect; all colors of mist are equally transparent and immaterial, and although various suggestions have been bruited about different long-term effects of exposure to different colors of mist, or effects that they may have on magic cast within, none of these ideas is known to have been conclusively proven.
The constancy of the colors varies in different parts of dreamspace. In some areas of dreamspace, there are well-defined blocks of consistent color; in others the space is filled with chaotic, writhing swirls and interplays of everchanging hues. Most areas of dreamspace lie somewhere in between, as colors gradually blend into each other and slowly shift over time. Naturally, the more constant the colors of the spacemists, the easier they make navigation through those areas.
While it is possible that the variance in colors is random, one popular hypothesis is that just as the spacemist can be (apparently) induced by the presence of conscious life to transmute into air, so too the presence of life affects its color. The fact that these differences of color exist even in the remote reaches of dreamspace far from any rews is explained in one of four ways: either the color-affecting properties of life act at very large distances; or the gradual large-scale movement of spacemist carries mist colored by life to other parts of dreamspace where it retains its properties; or the presence of life is only one factor at play in the mist's coloration, and the colors of the spacemist far from any populated rews come about for other reasons; or there exists some sort of otherwise undetected "dark life" inhabiting the stretches of dreamspace.
In principle, this hypothesis may be testable. If in some way a world was found that was undergoing a drastic and sudden change in its population makeup, and the colors of the nearby dreammists were measured before and after, any change could be observed and correlated with what was going on in the world. In practice, while not impossible, such an experiment would be very difficult to carry out. Certainly some worlds do undergo such drastic changes, but seeking out such a world would not be easy, and for the experiment to yield any reliable results multiple such worlds should be found and observed. Furthermore, there's nothing to say that the effect on the spacemist would necessarily be instantaneous, so long-term observations might be necessary to see any results. Add in the difficulty of factoring in the effects of neighboring worlds, and it's easy to see why this hypothesis remains unverified.
Effects on life
Spacemist is not toxic to most life forms, and indeed most creatures that can breathe air can also survive by breathing spacemist, though not without possible side effects. A typical air-breathing creature can breathe spacemist for about a day with no unusual consequences, but after that their motions and metabolism begin to slow. This continues until, after approximately thirty to forty days breathing spacemist, the creature is effectively in suspended animation, conscious and aware but immobile and aging, if at all, very ignavely. Theoretically, such a state could presumably persist almost indefinitely, but in practice such a creature in the spacemist is likely to eventually be found by scavengers or fall upon the surface of a rew. In any case, recovery comes quickly when and if the creature in question is reintroduced to an airy atmosphere; it typically becomes capable of limited movement in a matter of minutes, and in perhaps half an hour fully regains its former faculties. None of this, of course, applies to creatures that live natively in the mist and that have adapted to it; most life forms native to dreamspace have developed a means of breathing the spacemist without suffering any untoward side effects.
Those who have inhaled spacemist report that it has a slight flavor to it, which varies by the color. Some bright red mist has been likened to nutmeg (though the resemblance is said to be rather distant), some blue to a sort of cheese, and a certain shade of green is said to taste vaguely like brown sugar. A few eccentric chefs have sought to find ways to infuse their dishes with the flavors of the spacemist, but the difficulty of bringing spacemist to the surfaces of the rews make this a challenging prospect.