How to add alkaline to a drink? 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!
I had a look at the actual scientific paper describing the use of this substance as a pH indicator and a few other blogs, this is the overall advice:

1 - Please make sure that the FINAL pH of the solution is NOT basic-ish. This will not sit well in your customer's stomachs if they consume a full dose of a cocktail (120-150mL) with a final pH of more than 7.5. As I mentioned in the comments, there is a reason why you don't ingest toothpaste. Basic substances also leave a very unpleasant mouthfeel - it is a mix between a very tannin-ish feel and corrosive irritation.

2 - Do NOT add Alka-setzer. One person tried to do that and it ended-up being a gray-white shade, very unappealing for food and/or drinks

3 - There is not enough documentation on the REVERSIBILITY of this process (not all pH indicators are reversible), so you're going to need to experiment with it

4 - Aim for a final pH level of  5-6, this is where the blue color is at its optimal level. I suggest using CaOH (pickling lime / limewater) because that's easy to handle and nearly flavorless. Note that this is used in a lot of clarification processes, so you need to choose mixers that are low in protein so you don't get nasty precipitation when you add your limewater.

Reference:

The Butterfly Pea Flower as a pH Indicator