This freaky phenomenon just occurred a few minutes ago, while surfing SDMB.
I am wrapped in a camel blanket (brightly coloured sheet of cloth with a slit in the middle to fit over the camel’s hump that you can buy for around US$5 here - make great ponchos and tablecloths!) and drinking some weak Ribena (blackcurrant cordial) which is a pale red colour.
Anyway I spilt a couple of drops on the bright red stripe of the blanket, and it has gone black. I don’t mean a dark, wet colour, I mean an actual colour change red->black. Just like black ink that has leaked from a fountain pen.
Now as I look at it where it’s drying it is fading black to red (it’s a browny-shade now). Putting a fresh drop beside it again proves that the initial colour is black.
What could be in Ribena, and what could be in my camel blanket’s red dye, to cause this?
Could it be the alcohol acting as a solvent on the dye in the blanket? I suggest running some experiments with other forms of alcohol. Although I’m not sure why you’d even have any available in Dubai 
The red/purple pigments (anthocyanins I believe) blackcurrants (also things like beetroot) change colour like litmus according to the PH; I suspect that the blanket has some (alkaline) soap residue on it; this changes the pigment to a deep inky blue-black (acidity turns it blood red).
Ah - that might be it - I did wash the blanket not long ago so and my laundry ususally still smell of soap powder when it dries.
It doesn’t work with water, I checked.
Plenty of (legal) alcohol all over Dubai! It’s not forbidden here, they just won’t sell it to Muslims.
You can do the experiment with a three glasses of Ribena; add a teaspoon of vinegar to one, a pinch of soap powder to another and leave the third alone; stir them and compare the colours (you might not want to drink them all after this though).
What kind of freaky place do you come from where Ribena is alcoholic?.. Ribena is a brand-name for blackcurrant cordial… non-alcoholic ‘squash’ we call it in England, I think americans might say ‘Gatorade’ or something similar…
I assumed that this was either a casual remark not connected to the topic (perhaps sheepishly accounting for drinking Ribena) or a language confusion between alkaline/alcoholic.