I usually just let the green ones block the arrival of any more advanced ones. If you transcended once, you won't even need a single Neuron before you've reached the auto-killer.
i've transcended at least 3 times and the pink ones (the ones after purple) arrive before i get anywhere near the 5M cells needed to start producing enzymes, the pink ones usually are between the 1st and 5th overall spawn of the Xenocytes, e.g. 1st xenocyte spawn = green, 2nd spawn = green, 3rd spawn = pink)