Holiday food. Your washing machine is cowering.
Take a deep breath, and know it will all come good. First of all, linen is a bast fibre, and doesn't take stains deep into the thread. Secondly, a drop or two of hand washing-up liquid rubbed into a greasy mark works wonders, and thirdly, even bad stains tend to come out with repeated washing. My best tip? Don't tumble dry a stain, as heat can set it.
Light colours versus dark? Whites can be bleached, but dark colours are more forgiving in the moment, and can ease the guilt of whichever guest upturns a full glass of port.