What kind of graphic adapter is in the embedded system?
You probably need to look in the kernel source/docs to find out how that specific adapter works.
Perhaps you can try this kernel module for Nvidia:
There is something called matrox-tools which should work with Matrox cards:
# apt-get install matrox-tools fbset
tweak contrast, saturation, hue and brightness:
# matrox 0x1e 0xd0
# #matrox 0x20 0xff
# #matrox 0x22 0xff