you will need to shield the ribbon cable again on the back plate.
when you remove the old ribbon cable you ruin the shielding in place; without that shielding you will experience issues with odd screen colours and with the digitiser sensitivity (especially in the upper third)
for shielding you can use standard electrical insulation tape.
just cut a strip long enough and tape it along the length of the ribbon cable.
also be very careful with the lcd connector; its very flexible and has to be exactly in place for your screen to display perfectly; usually it gets bent slightly when you remove it; so just check it; carefully flex it back and be 100% sure its sitting perfectly in its slot before pressing it down again. even a slight misalignment will result in pixilation, discoloration or an odd stripe.
dunno why but the iPhone 6 and 6+ lcd connector is just rubbish.