I tend to agree with Flightluuvr-
On those aircraf that are white, cost is likely one of the deciding factors.
A few years ago the NYPD changed the livery of its patrol cars from the old Blue base with white lettering, to the current white base w/ blue lettering. The reason given was the cost of the custom blue paint was too high, and much less is required to do just the lettering.
Now imagine how much more paint goes into an aircraft, and the cost of the basic paint, being that its formulated to withstand the rigors of aviation.
Im not an airframe or paint guy, or an accountant though, so its just my opinion.
A lot of money by the time your done, no matter what color you paint the things!!