Soil Turning Green?

Recently 1 of my friends seedlings that is about 5" tall has been showing a green "Moss" Type look at the top of the soil, very dark green and hard to notice unless you compare against other soil.

Strange thing is hes got 5 other seedlings in exactly the same soil and this is the only 1 that has anything green going on

Anybody know what this is? Algae or moss/bacteria of some kind? Fungus?

whats the airflow like in there?
and humidity levels, sounds like moss/algae shit =/, hay you never know it oculd be sum special type of moss that helps break down nutrients so your plants absorbs them better XD
.....but i doubt it

dont worry about it, its some kind of moss. i always have it cos i grow things in polytunnels, where the airflow is restricted.

lmao hopefully

ok kool il keep an eye on it still