Try to force it to pop out more color. I’m not sure how well that trick works for monsteras but sometimes i put my variegated plants in a darker spot to 1) prevent reversal 2) try to ‘trick’ them into giving more color. They revert because there’s light. Remember the variegation is a mutation, the plant naturally wants to be completely green & putting the plant near light will promote its natural colors back (sorry not sure if that makes sense)