Activity or result?
I've been painting.
- The activity itself
- Finished or not, it doesn't matter
- Look at the paint on me
I've painted it.
- The result
- The job is complete
- Look at the wall
Examples
My hands are dirty. I've been repairing my bike.
My bike works again. I've repaired it.
Ask what the sentence is really pointing at. The mess and the effort, or the finished thing.