I've recently become fascinated by the use of butterfly pea blossoms to add colour to alcoholic drinks. (Yes, I've been watching How To Drink on Youtube). It acts as a natural pH indicator--add lemon juice to blossom-infused gin, and it'll go from purplish-blue to pink.
The thing is, for Reasons I want to do the reverse! I'd like to make a slightly acidic beverage, then elevate the pH, so it turns purple in the glass.
I'm familiar with using e.g. bicarb to elevate pH in savoury cooking--for caramelizing onions, that sort of thing. But I'm concerned about the flavour effects on an alcoholic drink. Are there any edible ways to elevate pH that are flavourless, or would be easily masked by a cocktail?
If there aren't, would an Alka-Seltzer tab provide the right pH reaction? I'm not a chemistry person at all so I'm not sure if the acid-base reaction would provide colour change as well as the bubbles.
ETA: TLDR what I want to do is dye a spirit with butterfly pea blossom, add acid to turn it pink, then at the moment of service add (ideally flavourless) ____________ to turn it purple/blue again.
Thanks in advance, all!