I think you're right--that we'd have to ignore it--since Vulcans and Andorians (more precisely, the actors who portray Vulcans and Andorians) appear with pink gums and caruncles as well, even though in the Vulcan case they are explicitly said to have copper-based blood (regardless of the visual, bright-green evidence that suggests they actually don't ) and Andorians are explicitly shown to have a respiratory pigment that can virtually only be hemocyanin or an equivalent copper (II) oxidation compound. It even oxidizes, becoming dark blue, in air, just like hemocyanin in earthly animals does. On the other hand, "City on the Edge of Forever," "Patterns of Force," "Piece of the Action," Star Trek IV, and "Carbon Creek" all seem to think that a being that by all rights should have green capillaries or at least should not have red capillaries can walk around like it's human, or one of humanity's unaccountably many cosmic copies, and no one would notice. And this is just baffling. Anyway, I'm pretty sure I've seen Cardassians bleed red--I can't recall an instance where their blood hasn't appeared red. As others have noted, the Bajoran ability to carry both Cardassian added to the fact that they can also carry human fetuses completely rules out biochemistries that we would find exotic. Regardless of The Final Frontier's presumably symbolic flashback to Spock's live birth, Amanda Grayson could not supply Fetal Spock with oxygen with hemoglobin. Neither could Kira Nerys have supplied oxygen to Fetal Toshiro O'Brien without hemoglobin, and since presumably Tora Naprem has the same respiratory pigment as her distant relative Kira Nerys, Fetal Tora Ziyal must have been nourished with hemoglobin. Furthermore, if Bajoran blood--which is definitely red--and Cardassian blood have obviously different colors, the Obsidian Order's deception in "Ties of Blood and Water" would be exposed in a (literal) heartbeat, since all Kira "Iliana" Nerys would have to do to prove that she was by no means Cardassian would be to bleed. Genetic testing and such could be influenced because no one directly involved was competent to perform it, but surely Tekeny Ghemor, despite being a little bit naive, can still tell the difference between red and orange or green. Even ignoring the evidence, all things being equal, I'd say that Cardassians should have hemoglobin or a similar iron oxidation pigment, since hemoglobin is superior at bonding oxygen to hemocyanin on a molecular level. On the other hand, hemocyanin need not be contained in blood cells, potentially creating a greater carrying capacity in bulk. The trade-off here is stamina, as the viscosity of blue blood with the same carrying capacity as red blood would be very high, placing great strain on circulatory systems of similar design, and at least requiring much more energy to transport. I find it very difficult to believe that Enterprise got this right on purpose, but they did get it right. I think Cardassian blood would be visible through the skin. They may not blush to show embarassment--as I think you may want to show, Nerys--because they're aliens and it's a wonder enough that they smile to show happiness (a trait that we would consider vanishly rare on Earth, if weren't we that had it ). However, I strongly suspect that Cardassians would use their blood as a radiator just as many earthly animals do. That we don't see flush Cardassian faces can be readily explained because we rarely if ever see them in environments they find uncomfortably warm. Dukat claims the Breen slave planet,whatever it was called, has great weather, possibly just to be a jerk, but we cannot rule out the possibility he honestly thinks a roiling desert is a nice place for a stroll. Probably a good 90% of the time, the only Cardassian we see is Garak, and he's usually bundled up and by his own admission always uncomfortably cold. In conclusion, Cardassian blood is 100%, without a doubt red.