Natural colors can be separated into two groups, the ones that are dependent to pH and the ones that are not. As in red cabbage, purple basil and pomegranate (from left to right in the photo), pH dependent colors originate from similar compounds that give different hues according to the pH. The scale changes from blue to red in accordance with increasing acidity.
This was one of the most challenging issues during my testings. Although the colors are impressive as pinks, purples and reds while they are still in the plant body, they are not good at dyeing cotton fibers. The main reason for this is that cotton fibers don’t have enough affinity for dyeing molecules in an acidic bath. Thus, I decided it wasn’t a good idea to use pH dependent colors.
However, there is an exception for this just because nature exists with its exceptions: safflower, Carthamus tinctorius. It is possible to get both yellow and pink from its orange flowers by altering the pH. Here is the exception that it possesses: although pink is obtained by acidity, it can dye cotton cloth with satisfying fastness.