A solution contains both phenolphthalein (pKa=9.3, colorless when protonated, pink when deprotonated) and bromophenol blue (pKa=4.0, yellow when protonated, blue when deprotonated). The solution pH is adjusted to 5.5. Which observable color is most likely?
a) Purple (combination of pink and blue)
b) Blue
c) Colorless
d) Yellow