poplar project continues and grows

[hopm]

I made a post awhile back about running some poplar for trim in my daughters house that is currently under construction. My plans were to prime and paint then top coat once installed. Things have a tendency to change in a hurry round here. Her and my son in law both really liked all the colors in the poplar and have decided they would like to use on their stairwell walls, ceiling over stairwell, and a vaulted ceiling on 2nd floor that is basically a large living area that extends into 4 dormers. They want all of this in a natural finish. In the past I have done pine this way and usually put a very light white glaze and finish with waterborne urethane. Will this work to keep poplar from darkening also? i want to avoid any ambering but i dont have any experience with poplar other than paint. Are there any quirks I need to know in advance? 
Thank you for your response!!

[Autocar]

Natural finish has been my favorite also