I'd this entrusting on the back glass

[MikeB]

At fist I was hoping for coralline as it started.  It is green and very hard was hoping for it to colour up but no luck so far

 

[KBennett]

Looks like coralline to me.  It'll turn pink.  Be patient. 

 

[reeffreak]

That's coralline algae.

 

[MikeB]

Ok that's guys. Glad I did not scrape it all off

 

[KBennett]

Mine was all kinds of different colours at first.  It's all pnik, purple, and red now.

 

[Boga]

If it is green and the shape of coralline, then it is green coralline. It is not a very common type. I had it in my old tank and it was carried to the current one as well.

I posted one picture on link below. You can see some green/lime colours.
http://www.thefragtank.ca/forum/index.php?topic=6654.0