If you don't plan on getting a
tonneau cover, I think you should stick with black LINE-X. The bedliner has a texture and dirt, sand, and other junk tends to stay in the texture (unless you clean it all the time). So, if you get white, it might just look dirty all the time. Now, if you plan on getting a
tonneau cover which would keep a lot of junk from falling on the bedliner, then white would certainly be OK.
If you get black, be sure to get the optional LINE-X Xtra product which prevents fading.