is not sensing e.g. a colour like something? i'm slightly colour blind, and i can assure you that i "see" all colours. of course i'm seeing something people will full colour vision can see. but if the colour of some particular red patch is like something, and that seeing a grey patch is too, then is that not enough to think that not seeing its redness is too? the reply could read that people with colour vision have an identical qualitative experience as the colour blind, but with a little bit more, and so being colour blind is not like anything at all - except having vision, seeing shape and form. but it does seem to me that darkness is like something, in addition to the absence of light, and so why not greyscale or whatever?
we can maybe imagine someone who was never able to blink