Place two heat-safe bowls or containers (I like to use glass) on your worktop. Sprinkle the beet powder in one and the butterfly pea flower powder in the other. Halve the vermicelli noodles and place the noodles in the two containers.
Pour boiling water over the noodles until they are submerged. Soak until they're tender, about 5 minutes. One at a time, drain your containers of noodles and set them aside to cool in separate containers or bowls.
In a small mixing bowl, whisk together the soy sauce, toasted sesame oil, fish sauce, lime juice (don't wash your hands of the lime juice!), and maple syrup to make your dressing.
Toss ONLY SOME of the blue noodles gently with your hands so that the lime juice transfers to the noodles, making the blue anthocyanins from the butterfly pea flower powder turn from blue to purple/fuchsia. You want to leave some of the noodles untouched so that you have a gradation of hues. Wash your hands to remove any lingering citric acid.
In a large mixing bowl, combine the cucumber, radish, cabbage, and cilantro (reserving some for garnish), and toss them all together.
Add about 3-5 Tbsp of the dressing to the salad and toss to combine. Make sure that the salad is just a little bit over dressed (this will balance out when you add in the noodles).
In a large mixing bowl, combine most of the pink and blue/purple noodles together, leaving a small handful of each for later.
Transfer the dressed vegetables to a large serving bowl, then add the majority of the pink and blue/purple noodles and toss together.
Garnish with the reserved noodles (which will be more vibrant since they haven't come into contact with the dressing), crushed peanuts, sesame seeds, radish slices, and remaining cilantro leaves.