I checked on my P. imparis and one tube has the cotton and water turning purple.
I've seen black spots in cotton before, but have never seen things turning purple before.
Do I need to change tubes?
EDIT: Okay it's pink in full spectrum sunlight. A nice pretty watermelon pink. 
Edited by OhNoNotAgain, May 28 2020 - 5:11 PM.
Past & Present
Veromessor pergandei, andrei, stoddardi; Novomessor cockerelli
Camponotus fragilis, Camponotus sansabeanus (inactive), vicinus, laevigatus/quercicola, CA02
Pogonomyrmex subnitidus, P. californicus (inactive)
Liometopum occidentale (inactive); Prenolepis imparis; Myrmecocystus mexicanus (inactive); Tetramorium sp. (inactive); Lasius sp.
Termites: Zootermopsis angusticollis, and a box of drywood termites that can't be seen
Isopods: (most no longer keeping) A. gestroi, granulatum, kluugi, maculatum, vulgare; C. murina; P. hoffmannseggi, P. haasi, P. ornatus; V. parvus, P. pruinosus, T. tomentosa
Spoods: (no longer keeping) Phidippus sp., other