Dark matter represents far more of the universe than 'light' matter by volume if our physics is correct, so by that most galaxies are mostly dark matter by default. We have found a few very small ones that don't seem to be.
With this said dark matter still influences the curvature of space time so its not completely invisible. We could see a dark galaxy because it would alter the images of galaxies behind it with things like Einstein rings and crosses.
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Depends exactly how your phrasing this.
Dark matter represents far more of the universe than 'light' matter by volume if our physics is correct, so by that most galaxies are mostly dark matter by default. We have found a few very small ones that don't seem to be.
With this said dark matter still influences the curvature of space time so its not completely invisible. We could see a dark galaxy because it would alter the images of galaxies behind it with things like Einstein rings and crosses.