A Brain teaser!

[Just call me MJ]

hello everyone! I love brain teasers!
now lets play
the one who answers the brain teaser posts the next teaser!

I'll start!

I am round but not always around,
Sometime I'm white, sometimes I'm black, sometimes I'm both.
what am I??

 

[CaptainDanger]

You can post here about it : http://www.xtremepapers.com/community/threads/brain-teasers.11667/ No need for another thread!