It would be useful to have a layer to indicate tiles which are tilled but not-yet planted.

You can see missing crops in the current crop layers, so not sure we need a dedicated layer:

Yes, that's correct. However, it's pretty hard to see (especially in non-rectangular fields) and right now I'm not sure if what you showed in the screenshot also applies to non-tilled soil.

Yep, it does. Crop layers highlight crops in red or green, so any missing crops will appear as a hole in the color overlay.

Note that it's only a quality of life thing, and shouldn't be high priority. I might implement it and send it as PR.

Yes, but the hole in the color overlay is also present on non-tilled soil.

The question to be answered is: "Is there any tilled soil where I forgot to plant stuff?"

I did an initial implementation on the tillable layer. What do you think? Does that make sense?

Thanks! Added in the next Data Layer update.

I made a few tweaks: