iPhone 4s jumpy screen, paletized colors

I have an iphone 4s (verizon) that has recently gotten a jumpy screen. For a while (maybe 1 year), it had a palettized color issue where some colors appear pink. Recently, the screen has started jumping. See video:

See image:

This is something I bought used, but appears to not have been water damaged. Further, I keep it in a lifeproof case, and am pretty gentle with it.

Even when the screen is jumping, the keyboard appears to work fine. I.e.: if I enter text where the keyboard would normally be, the letters/words come out right. Therefore, I think the digitizer is OK.

I took it to apple recently to see what they thought. Unfortunately, it wasn't jumping, but they at least saw the pink. After a few questions, apple said they thought it was the motherboard, and that merely replacing the screen wouldn't help.

Anyone have any thoughts? I'd rather replace the screen for $35 than replace the phone.