How to unify the color and brightness measure of two given cameras?
Here you have two options.

1) Color calibrate your cameras (radiometric calibration) to the same reference. Then try matching. There are many academic works on this topic, one of them being:
http://research.microsoft.com/en-us/um/people/yasumat/papers/rankcalib_PAMI12_preprint.pdf

2) Use a vignetting invariant (or color invariant) feature descriptor. For example you could try to work with gradients instead of intensities and so on. This is harder, but if you could achieve it you get rid of the cumbersome calibration procedure. There are also valuable works done in this field, such as:

http://www.cvip.louisville.edu/wwwcvip/research/publications/Pub_Pdf/2006_2/CSIFTA%20SIFT%20Descriptor%20with%20Color%20Invariant%20Characteristics.pdf

Good luck,