Purple/blue Algae?

HI I have a tank that was active as freshwater for a few mounth and then it was empty for about 3 mounths. He was at my friends house and today I transported it so I saw it the first time since ive emptied it and it has those weired growth in a blue and purple colors in the inner side of the glass.I'm afraied that some kind of chemicals maybe reached in although it relly looks like an algae growth pattern. What do you thing? did you ever ee algae in thI colors? When ive emptied the tank it had green and brown algea. Also worth metioning that about 1 year ago this tank was a saltwatre tank .

 

So is there water in the tank or is it still empty? Looks like mold from the photos.

 

empty for the last 3 mounth.. mold? purple?

 

In other forum people told me it looks like a dried algae that origin in saltwater

 

If there is water, you can get mold, and it comes in all kinds of colors. That's just what it looks like to me.

 

but its empty for 3 mounths

 

But it was wet at one point, so it could have grown mold. It's really hard to say exactly what it is though.