White patch on dorsal of blue grass fish?

[netty_3164]

Hi all,

Last night I spotted that one of my guppies have a strange white patch on its dorsal fin?

There doesn't seem to be any protrusion when viewed above.

Not sure if its a colouration thing but I have never come across a blue grass with white dots?

Anybody able to identify this/experienced it with their fish?

Cheers,

John