Green Perlite?

I was wondering if anyone knows what is up with the perlite in some of my pots turning green. I have about 30 plants and only one is not healthy- stunted growth and thin dry leaves, and i notced that the perlite in that pot had a green hue. There are a few other pots that are greenish and doing well but most have no green at all. I dont think it is mold but not sure so how do i know/ what should i do/ any ideas?!. Thanks

Plants are outdoors, 4 weeks old, 8 inch tall, in 6 inch pots, potting soil and perlite 50/50 mix.

If the soil is always wet you will have a green alge layer, could be mold? need a pic. perlite holds water so if you have a soil thats always drenched in a humid place shade has alot to do with it, you could run into root rot. dont water for a couple of days, if the soil in that container is really packed cruch the sides slightley to allow air and root movement.

It's just algae. Cover the top of your pots so light is blocked and it will die.