What causes graphics to change colors and flicker?

I would imagine you are pressing opposite the VGC (video graphics chip) These are notorious for developing cold (cracked or lose) solder joints over time because: a)EPA rules have changed the composition of "acceptible" solder and b) these chips get very hot, and cool down often.

The problem is that it's not easy to correct that fault. Some have had some luck making and inserting a shim (substitute finger) to press on the spot (using stacked paper, fiber, plastics, coins, washers have all been used) between the case (inside) and the logic board... eventually these also fail but sometimes they can extend the useful life of the unit by months, even years.

Re-soldering the chip is expensive as it requires complete dis/reassembly of most of the computer, special tools and solder.

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