Germination
No, I have not encountered a light green mushroom growing in my plant.
Give the plant proper lighting (preferably sunlight) and water. Make sure the plant you are growing is also a green plant.
There really isn't enough information to answer your question. However, if you mean a green plant and CO2 gas then you generally get a faster growing plant.
The type of plant that has red and green leaves is called a coleus plant.
A tall plant with red flowers and green leaves is called a hibiscus.
The green pigment in plants are called chlorophyll.
Phototropism
yes
IT is called "Chlorophyll" and is found in the "Chloroplasts".
harvest
It is called the seedling.
To prevent green mushrooms from growing in your plant, ensure proper drainage, avoid overwatering, and provide adequate air circulation. Remove any decaying organic matter and regularly inspect the soil for signs of fungus.