Deric Bownds in Mindblog has a post on the book ‘The Ego Tunnel’ by T. Metzinger (here ). An excerpt on the ineffability of consciousness is included:

In between 430 and 650 nanometers, we can discriminate (make same/different judgments about) more than 150 different wavelengths, or different subjective shades of color. But, if asked to re-identify single colors with a high degree of accuracy, we can do so for fewer than 15. The same is true for other sensory experiences. We can discriminate about 1,400 steps of pitch difference across the audible frequency range, but we can recognize these steps as examples of only about 80 different pitches… Thus we are much better at discriminating perceptual values than we are at identifying or recognizing them.
Metzinger uses a simplest example of two similar shades of green to spell through the consequences of this situation (he calls them Green No. 24 and Green No. 25, nearest possible neighbors on the color chart, such that there’s no shade of green between them that you could discriminate). We can experience their difference, but are unable consciously to represent the sameness of Green No. 25 over time. We do not possess introspective identity criteria for this simplest state of consciousness, and we can not pinpoint a minimally sufficient neural correlate of Green No. 25 in the brain if we can not correctly identify the phenomenal aspect of Green No. 25 over time, in repeated trials in a controlled experimental setting. This is why it may be impossible to do what most hard scientists in consciousness research would like to do: show that Green No. 25 is identical with a state in your head.
These simple findings show that there is a depth in pure perception that cannot be grasped or invaded by thought or language. This ineffability problem arises for the simplest forms of sensory awareness, for the finest nuances of sight and touch, of smell and taste, and for those aspect of conscious hearing that underlie the magic and beauty of a musical experience. It almost certainly appears also for empathy, for emotional and intrinsically embodied forms of communication.

What is being said here? We know that experience is ineffable – we cannot describe it completely because language has a ‘coarser grain’ then experience. That is not a surprise. We can notice that two things experienced together are slightly different without being able to identify or recognize which one is experienced alone later. That means that memory too is more ‘coarse grained’ than experience and that too is not a surprise. What does it mean to ‘show that Green No. 25 is identical with a state in your head’? (I hate talking about states of mind or brain so I will talk about processes.) There can still be a process that is identical to the experience of green25 and also a process that is identical to the memory of having experienced green25. It would in fact be surprising if these two processes did not differ in some ways.