I also think it's because of the cable. I am using a VGA cable but for the moment I am using the old Radeon HD 4670 so it's ok. When I use the Fusion APU, if I make screenshots, the images look ok on another computer, so it must be a problem of communication between computer and monitor - most probably the cable, yes. I will try with a DVI cable as soon as possible.
I have a 7560 and a MSi FM2-A75 and in the bios I can set the mem size
there is an PEG/IGD option when it is on forced IGD I can set the size up to 2GB (current at 1GB)
Maybe all motherboards do not have this option
To get the Catalyst driver to show clear on hd 1080p tv via hdmi (Not sure if its related to your problem) In catalyst, expand the '+' for DTV HDMI
then click on scaling options and set to 0%
then click on Pixel Format and set to full rgb