Watering your moss
Moss loves a humid environment, so you should keep it in closed terrariums rather than open terrariums. If you choose to put moss in open terrariums, it is very important that you spray it regularly with filtered, distilled or rain water. Rain water will be always the best choice when watering your moss. Tap water contains too much chlorine and can turn your mosses brown.
Amount of light
Moss requires the same lighting as your enclosed terrarium. It should be placed in indirect light. It should never be placed in direct sunlight, otherwise moss will lose its green color.
Help, my moss has lost its green colour
If you notice that your moss is turning yellow and losing its color, you should take action to prevent it from spreading. There are a few reasons why your moss is behaving this way.
First, it may be because it is receiving direct light. Check where you have placed your moss and move it to another location with indirect sunlight if necessary.
Another reason could be that you did not press your moss well to the soil when you placed it in your terrarium, and therefore it cannot absorb nutrients and moisture from the soil.
If the moss has lost its bright green color, it may need to be watered. If you suspect it is suffering from a lack of water, check the feel of the moss by hand before watering and if it is dry, water it with filtered or distilled water.