I have read this ELL question and this ELL question but isn’t clear to me how the “though” word is used in this sentence. Is it used to show selection? (I say the blue one) or other meaning is applied?
Which piece will be used for this experiment?
Ideally both pieces would work, though blue if you only have time for one.
Though in your example is used as a conjunction to mean but. The sentence means that ideally both pieces would work, but if you only have time for one choose the blue one.