I know a number of carriers have painted the slide arming handles yellow to avoid confusion.
Could the carrier in question implement a cross-check procedure? Where there are two cabin crew one "gets" door L and one door R both crew members must confirm the sides are disarmed on both doors before the door can be opened on-stand. Where there is one cabin crew at a door a call-back procedure could be implemented. (I've seen what I best describe as a "confrence call" on the A321, for example) each member needs to confirm "their" door is armed/disarmed before doors can be opened.
Another option would be to implement a "crew yellow selector handles - disarm" call to be made once on-stand, or just before it. Either made by the No.1 or flight deck.