READ THIS FIRST:
Here at Kazyeh, we do not share the view of whers expressed in the books Dragon's Kin, Dragon's Fire, Dragon Harper, or Dragonsblood. These books not only contradict themselves in several places, but show a blatant disregard for the pre-established canon formed by the rest of the Pern series. To be blunt, Todd McCaffrey's works are a black mark on the good name of Pern, and will be, for the most part, ignored.
DO NOT present anything from within these books as canon to this game. These are the rules we adhere to. Whers do not fly, they do not eat Thread, and they definitely do not see in heat-vision.
That said, hopefully you will find the following information enlightening.

Whers

The watch-whers of Pern are the result of a failed experiment by Wind Blossom Ping, an attempt to expand on the work of her mother, Kitti Ping.
While they resemble the dragons in terms of color and the fact that they form a mental bond with their handlers, the similarities generally end there.

Whers are considerably smaller than the dragons, the metallics standing at around the size of a large draft horse, with the smallest of the greens usually being no bigger than a pony.
They are photophobic in nature, as they lack the faceted eyes of the dragons and fire-lizards. The lack of facets directs too much light into the eye during daytime. Glow-lights and weak firelight are generally tolerable. Because of their light sensitivity, whers are primarily nocturnal.
While vision during daylight is painful, the shape of their eyes gives them keen night-time vision, making them useful as guards. Their sense of smell, also, is superior to that of most other Pernese creatures.

Although whers can impress to humans, they are unlike dragons in that they do not have to impress. If a suitable, impressionable mind is not to be found, a wher will go wild. Wild whers are often sneaky and can be quite violent, making them a danger to humans. Likewise, if a wher is not closely bonded to its handler, it may go wild at any time.
Also, unlike dragons, whers can change bonds after impressing once before. Such is often useful after a wher-handler dies; Their wher, if still young and of sound body, can be re-impressed by another. Likewise, although rare, it is possible for a wild wher to impress itself upon a human, long after hatching.

Whers do not select their handler by gender, like dragons do. Akin to the fire-lizards, they will impress to either gender, whoever happens to be close at hand during their hatching.
Whers will often take an 'impressed name' for themselves after hatching, usually the first two or three letters of their handler's name, followed with -sk. Not all handlers call their whers by such a name, and wild whers select names for themselves that do not necessarily end in the -sk suffix.

Whers have stunted wings, and as such, do not fly. Whether or not a wher can breathe flame is indeterminable.
Since whers cannot fly, they do not mate in flight, but instead hold long 'runs' where the males are challenged to catch a female in order to mate with her.
Wher clutches are small, and few of the eggs clutched are strong enough to hatch.
Both green and gold whers lay eggs, unlike the dragons. If bred by a bronze wher, a green wher may potentially give birth to a bronze in her clutch, but she will never lay a gold.
Gold wher eggs are unmarked, and indistinguishable as a gold egg.

Simple overview:
Gold - Female; Lays clutches
Bronze - Male
Brown - Male
Blue - Male
Green - Female; Lays clutches