The reveals of the bitch base cabinet are the same whether you use the Ikea doors or the custom doors. We have used a number of Hallarum (dark brown/red color) from Ikea with the birch base cabinets and it has not been an issue. If you use an natural Oak color like what is in the photo it is less of a concern because the colors match better. If you go with black/brown custom stained door fronts, it will be slighty more noticable if one is really picky. If the doors are made and installed correctly, it is not a problem even with black/brown.

I think this solution is by far the best bang for the buck when it comes to cabinetry. Don't think you are getting a Bulthaup engineered cabinet system with this approach though.

I would buy a sample white door (the cheapest one) for each size you need and give to the millwork guy to reproduce. This will take the guess work out for them.

Previously captain jack wrote:

specifically, I am concerned about a "two-tone" look.  with the custom doors surrounded by reveals of the cab. box finish and sides of boxes not matching the custom doors.

do you mount the door hardware yourself or give the shop a standard door so they can mortise out for the hinges?