Yellow fungus/mold on soil in container plant

[NeoDevin]

I have an orange tree growing in a pot, and lately the soil has been getting some yellow growth of some sort on it. I can't seem to find anything about it in any of my books. The plant doesn't appear to be adversely affected. Any ideas what it is? Is it a problem? Will it spread to my other plants?

 

[wolram]

Is it a form of moss.
Can't see pic yet, but this is yellow moss
http://gb.123rf.com/photo_2129926.html

 

[hypatia]

Remove the plant from the pot. Remove the top 2 inches of soil, might as well check to see if its root-bound at this point. Spray the root ball with a mixture of 1/4 cup of cider vinegar mixed with 1/2 gallon of water{which should be room temperature}.
Scrub the pot with a brush, very hot water and more vinegar. Re-pot using a good quality potting soil.