I guess you mean sphagnum moss, which is usually sold dry and is a very pale straw colour in that state. You need to grow it in a cool place, it doesn't like heat at all. Temperatures over 30 degrees C during the day should be avoided as they will stress the moss and even kill it, but it can withstand them if it is very wet, in shade and if the temperature falls sharply at night. Night time temperatures should always be well below 20 degrees C. The moss has no problems with freezing temperatures and snow cover in winter and therefore the best way to grow it is outdoors in a cool, shaded spot. The moss that is commercially available comes from cool/temperate regions of New Zealand, Chile and Europe. This moss will not grow in hot tropical climates.
The water MUST be as pure as possible and NEVER have fertiliser in it. The moss is very sensitive in this respect, so you need rain water or reverse osmosis water as tap water will kill it. Some sun in the early morning or late afternoon is ok, but it generally is best to grow it in a light, but shaded position. Even though the moss can be grown moist, it prefers to be soaking wet.
I find that if you take two or three big handfulls of the dry moss, put it in rain water or reverse osmosis water and treat it as outlined above, it will germinate and start to grow on its own as there are always some spores left in the dry moss. If your moss gets covered in green goo before it has a chance to germinate and grow, then you used water that had too many nutrients in it , which allows algae to grow and outcompete the moss. Healthy sphagnum moss that is alive has a naturally low pH and will kill most microbes including algae and therefore does not get covered in algae.