The long awaited MacOSX 10.6.7 update is finally available through Software Update (313 Mb). It notably enhances graphics stability and fixes flickering problems on recent macs when using some external displays.
However it does not fix the grays colors flickering problem on June, 2010 Mac mini (tested at least with a Samsung synchmaster 206BW display, using Apple’s HDMI to DVI). This could be tied with memory speed, as the Nvidia 320M chipset uses the main memory, however it is the same with the stock 2*1 Gb memory modules, or third-party 2*2 Gb and 2*4 Gb ones.
Some users suggest using the mini display port to DVI adapter.
As previously reported, Apple’s mini display port to VGA adapter does not experience flickering, however colors are over-satured, making it useless (with this same Samsung display). Colors seem better when using an Espon projector. Some people also reported that using a non-Apple mini display port to VGA adapter worked better.