I notice in your profile that you use Flexi. I use Flexi with my Mimaki as well, and I used to have that problem years ago. I'm afraid I don't recall the solution entirely, but we did resolve it. (I'm thinking it was some color management settings in Flexi that are over my head, and therefore easily forgotten) However I have one band-aid solution to offer for possible help in some cases. This will not fix it in all cases, but on some image files, where the only, or the most noticable white area of concern is the area surrounding an image (rather than dozens of inside contours of letters etc.) you can open in Flexi, then under the bitmap menu, open bitmap toolbar. From there you can access the magic wand & select the white area, then hit delete. As I said, for one big white bounding box around a colorful logo, this might be an easy fix... but if there are a bunch of letters where the middles all have to be selected, it quickly becomes not worth the trouble.
As for the real solution that I don't recall... I'm wondering if "whitepoint" has something to do with it.