Plums turning a bit grey in my brandy

I'm making a litre of plum 'brandy' which is mainly vodka with a dash of brandy. I halved some Victoria plums and put them in a sterilised kilner jar along with a pound of sugar. The vodka is going a lovely pinky colour but some of the plums are looking decidedly dark grey, almost a blacky colour. Would this spoil the finished product as i don't want mouldy plum brandy!! I'm wondering if it's where the plums at the top are oxidising a bit and where i'm giving it a good shake everyday, they are getting mixed about...

The colour from the plums is leaching into the brandy. Nothing can go mouldy when it's in alcohol

I work on the assumption that I wont go mouldy when the alcohol is in me.....