My project in Textile Dyeing with Natural Pigments course

I had been trying out textile dying before, having taken another online course, but I wasn't being organized with keeping data on my experiments together, and the present course inspired me to organize all I had in one place, so I only have little info on the methods, such as amounts of plant-matter used in each sample. I will try to be more diligent on writing things down now that I organized what I have.
Another thing I had not been experimenting with was changing the pH of the dyes, and now that I have started testing this, I have a few questions regarding changing the pH to get other colors. I have been using baking soda and vinegar to play with pH, as I haven't yet citric acid or cal at hand.
- The curcuma reacts very strongly to baking soda, turning orange and developing to deep red as it oxidizes. If I add vinegar ON TOP of Curcuma that has been changed with baking soda (Red) it turns instanly back into Yellow! BUT, if left sitting for a few minutes, the yellow fades and goes back to the previous Red. Why?
- Curcuma (pure) also reacts somewhat to vinegar, turning a brighter yellow. This also happens with Chamomile, even more noticeably, turning a much brighter yellow (with baking soda instead of vinegar!). Centrosema also changes in vinegar to a beatiful pastel pink. But I noticed a day or two later (or, in the case of Centrosema, just as it dries!), the baking soda/vinegar samples are the same color as the "untouched" pure dyes. Is this because baking soda and vinegar are poor pH changers?
- I also noticed in Curcuma, the red faded a lot when I put my sample through a hot iron, some of it came back, but why did that happen?
- The pH tests I did with Curcuma, I dyed all my samples the original formula and then, on top of that, added a pH changing substance ("overdying"): is this a less effective way of achieving those colors? (with Chamomile I dyed the baking soda samples in a separate vat where the dye already had baking soda in it) Is there a reason to choose either of these methods?
- My last question is regarding the durability of a dye that had it's pH messed with: how to make the fabric keep the pH-changed color, when it seems the fabric keeps reacting to other chemicals after the color is set? How to control the color on a garment, for example, if a drop of lemon juice can damage the color imediately?