How to extend vacuum packed pickled cucumber shelf life?

Color loss of cocumber is a common problem. First ensure following proper steps

1. Don't use metal like copper, iron, aluminium aur non food grade plastic as a contact surface during preparation.

2. Use uniodized salt preferably without anticaking agent.  (free of magnesium).

3. Proper blanching of cucumber add some amount of Potassium metabisulphite.

4. Soft water.

5. Remove blossom end of cocumber (source of undesired enzymes)

Beside these or if you are already following these then, a bit in detail

Chlorophylls, the pigments responsible for the characteristic green colour of fruits and vegetables, and there is general agreement that the main cause of green vegetable discolouration  is the conversion of chlorophylls to pheophytins by the influence of pH. The green colour of vegetables turns to an olive green, during this reaction, hydrogen ions can transform the chlorophylls to their corresponding pheophytins by substitution of the magnesium ion in the porphyrin ring. Find any suitable preservative to bind magnesium in pickle.

Hopefully this would help if not completely remove the problem.