When we investigate all sensations that imply "Nowness", and all sensations and thoughts that imply "Then-ness" or "Futureness", in other words whether a sensation, or a thought or memory of the past, or the sense of bodily contraction due to worrying about the future, whatever it is, once investigated we only experience all sensations as simply present and aware where it is. There is in fact, nothing inherently 'now', 'then', 'before', etc. These are simply impressions but when investigated all sensations that imply 'now', 'before', etc, are simply sensations vividly present where they are and are empty of anything inherent.
Furthermore, all our experience, be it thoughts, sensations, perceptions and so on, they are simply present, aware, non-dual as it is. This means all along, whatever manifests, be it sensations, thoughts, and so on, are simply manifest without an observer-observed duality. It is simply present and aware where they are. In seeing, always already only scenery, no seer. In thinking always already just thoughts, no thinker. In hearing always already just sounds, no hearer.
Similarly when we say 'awareness of grey', you may think that awareness is an observer of grey. Actually, the observer is the observed, or the observing IS what is observed, means there is simply the sight and sensation of grey. There is actually no separate observer or awareness apart from the arising sensation or sight which dependently originates. Means these sensations and thoughts simply arise and vanish moment to moment on its own accord due to causes and conditions. You did not create them (there is no you), nothing created them, they just appear according to the laws of causality. What we call awareness is simply the presently arising sound, thought, sight, sensation, etc. Hence you cannot say awareness is in the grey, as that would imply there is an entity called 'awareness' that can be 'inside' something else called 'grey', whereas in reality there is no separate or inherently existing entity 'awareness' other than these arising sensate reality itself.
Now with regards to attention, whether or not there is attention, sounds are still heard. If sound of airplane passes by, the sound will be spontaneously perceived whether or not you want to do so, and even if you are paying attention to something else like your breathe. Awareness simply awares of the entire reality all at once, as one seamless integrated totality. It requires no observer to observe, and there never has been a separate observer to observe. As for attention, attention is simply a mental factor that sorts of amplifies a particular sensations or thought. However attention is actually not what is 'aware' of sensate reality. All sensate reality are simply manifest in itself, aware and self-luminous in itself. The mind however focuses on a particular sensation. It is a mental factor, and as Shayne said,
when not thinking the attention dont exist.
when not focusing on a particular sense object the attention dont exist.
Now, while Shayne seems to put down attention, in Buddhism it is not necessary that attention is 'bad'. In fact it is important for certain practices depending on what you are practicing. Especially for classical vipassana practice, focused attention on sensations to observe their three characteristics is often important in the beginning stages. Attention is also necessary for normal functioning in our lives to certain extent. However, it is important to understand that attention is not an 'observer' of sounds, sights, etc. All sounds and sights and phenomena and thoughts are simply present where they are, self-luminous, without an observer and observed division.