Could you send me the camera apps list you tried? I would like to see how good they are.
Camera apps with white balance features:
Real Cam LE:
There are good ideas here, but poorly executed in practice--with book scanning, that is. This app's approach to white balance is choosing 1 of 5 points on the display that should
be white. But this wasn't effective on book pages and documents for me. So, if you could develop your own algorithm that allows the user to pinpoint white areas on the book page (even if the page appears orange from the lights, the pages are slightly off white, etc. where it calibrates the white balance as such) then that may help achieve a close color reproduction. What I also really like is the grid (book scanners will use this as a guide to minimize keystoned images on the page. And this leads me to another awesome feature for platen-hardware scanners: a level gizmo
built into the preview/capture screen. This is really helpful if you are trying to calibrate the angle of the platen (book page) with the angle of the iPhone's camera lens; if they are both resting at the same angle, then you shouldn't have resulting keystone problems. A completely square image.
Just released last week, I haven't bought this app to test yet until I see a few reviews, but it claims to have a white balance adjustment. The examples didn't show too much worth cheering about, but I suppose you never know until you try it.
Another cool app I like, but haven't put to work yet. It operates on a system of measuring the temperature of light in relation to a pure white surface. It is not a camera app, nor does it take pictures, but I do like this approach and the science about it. This means if the you could calculate the temperature of your lights on the scanning system, then, PageScanner could adjust the white balance accordingly.
So far, the color balance apps look quite limited. I thought I saw more apps with white balance features. I thought a couple apps I already owned have white balance, but they basically have B/W and Sepia toy filters.
...But virtual filters area good idea too. Setting up a series of a few filters to choose from, say, LEDs, Halogens, CFLs, etc.