Gravitons have frequency just like photons, and in principle they could be detected by methods similar to that of photons, by graviton absorption. However, the gravitational interaction is many orders of magnitude weaker than the electromagnetic interaction, so the probability of absorption is very small. That's why, in practice, it is very hard to detect gravitons.
Yes, gravitons have frequency.
They also have different selection rules for absorption (spin 2, not 1) and different sensitivities, because they interact with masses not charges.
Notably, the electronic excitations are much less sensitive to gravitons compared to the nuclear vibrations that are in infrared range. But not completely insensitive, because electrons have nonzero mass.
Gravitons in visual frequency range should duly excite retina, unless barred by selection rules. However, since they are otherwise weakly absorbed and refracted, they would not be focused - they would produce a diffuse glow no matter whether they pass through pupils, closed eyelids or skull.
I would note that in this context, there is not a material difference between the expected phenomenology if gravitational waves are classical waves (as in general relativity), or are instead point particles that exhibit wave-like behavior similar to that of photons (as in a hypothetical quantum gravity theory). In both cases, the frequency can vary.