Retro Look With Curves
Go to Layer → New Adjustment Layer → Curves and switch from RGB to
Reds. Then drag the line downwards a little for the shadows and upwards
for the highlights, creating a slight “S” curve. Do the same for the Greens.
For the Blues, drag the highlights down a little and the shadows up (for an
inverted S shape). The shadows should now be slightly blue-ish, the
highlights slightly yellow-ish.
Adjustment Layer: Curves