Delta Underside Colour

[BetaSingh]

Hello all
I am new to this forum so if I have posted this in the wrong place, feel free to move this thread.
I am going to make a Delta Connection CRJ 100, using the 1/144 BPK kit. As it is the new Delta livery, and has a blue underside, I was wondering as to what colour you guys would think best matches the underside of the plane. I would be very grateful if you could supply me with paint references.
Thank you all and have a nice day
Beta Singh