Hello,
let us assume we have a development system D01, a test system T01 and a production system P01. Then following is valid in case you create a new package on D01 and transport it to T01 and P01.
| D01 | T01 | P01 | |
|---|---|---|---|
| Source System | D01 | D01 | D01 |
| Blue Arrow Appears | No | Yes | Yes |
So as you see the source system will always be the system name of the development system (same as in ABAP by the way).
Normally you do not wanna change the source system in your transport landscape, but there is sometimes the need to do it. For example if you change your development system. If you go on a new development system, e.g. D02, it is necessary that all objects imported from D01 get the source system D02. This is necessary to be able to change the objects and to be able to transport them. You can do the change of course by a little hack, or the easier way, you set an alias system when you export the delivery unit from your original development system. So if you export your delivery units from D01, set as alias system D02. During the import of the delivery unit to D02, the source system is then changed to D02.
Best Regards,
Florian