I’m new to GP, please be patient ;).
I would like to change the color/pattern of an activity at a specific date interval.
main activity color is green and the date range from 01/10/2018 to 31/10/2018.
Is there a way to color the last 15 days of the activity (from 15/10/2018 to 31/10/2018) in red (or using a another pattern)?
Or is there a way to obtain something similat with GP?
No, sorry. Task is an atomic unit of work in GanttProject. If you need different properties for different portions, you have to create different tasks.