New Granite Patio - Staining through SBR slurry within a few hours - HELP!

Hi all, hope you are well.
During this lockdown I have started trying to lay my patio. I have chosen some silver grey granite slabs and have started to lay them.
Here is my process:

6:1 sharp sand and cement mix, this has a small amout of SBR mixed into it.
An SBR and Cement slurry is spread onto the back each slab. The slab backs were wet when I did this.
I attempt to lay the slab before the SBR slurry has dried.

The issue I am having is that I appear to be suffering from reflective staining almost immediately. The slabs start to darken withing a few hours of being laid.

I have attached some photos.
You can see the 3 slabs I laid yesterday, and the 2 large ones I laid this afternoon.

and here is the slurry mix being pasted on.

What can I do to stop this from happening, or is it normal to have this happen and will the issue go away on it's own?

Thanks in advance for any help.

It looks like usual moisture being absorbed into the slab.

See how it is in a few days when everything has set a d dried out.

Thank you. I will.

Very sorry to tell you this but we had the same issue and yes it does stain. You will not get it off. It's a bugger if you get in on anything. Our black slate slabs were really spoilt by this.