Cathay Pacific Asia Miles - Could I use the CX PINK card for LHR fast track arrival lane when I don't fly with CX

I got one PINK card for LHR fast track arrival lane but I did not use it; ecause the flight arrived before 5:30 am and the fast track did not open yet.

Could I use this pink card when I will fly VS Y and arrive at the LHR T3 next month?

Will the staff of fast track entry check my boarding pass or just recognize this PINK card with my landing card?

I know this is tricky but I just hope not to waste this card.

IME they have never asked for my BP... :)

It's extremely unlikely that they actually would know which flight you came in on, the only possible exception I can think of being if you use a CX pink envelope when there isn't a CX flight arriving for, say, 6+ hours. Even then, I doubt it. Be aware, though, that these pink envelopes are printed with the name of the issuing carrier because BAA charges the carrier for each use. So when you use one, CX will pay.

I think occasionally they change the colour of the slip as well. Is that true?

yes it used to be light pink and now it's like dark pink or purple so yes they do change it...but generally as long as you have a fast track pass, they will let you use it i dont think they are that strict about the timing of when u use it in the day, and with CX having 4 flight arrivals in to T3 a day....you shouldnt have any problem with them.....