AFAIK, BD only fives out the copper coloured BP's for SSCI, regardless of class (though this may be different for long haul). Business is still printed on the standard blue stock, albeit with the word "BUSINESS" printed repeatedly across the top of the BP.

LH uses yellow (tasteful!) for Y and C, with "ECONOMY" or "BUSINESS" printed as on the BD cards. First class get bright red (even more tasteful!) boarding passes.

SK are similar to BA in that they just print a different class letter (M/C) for each class of travel, and have a single BP design.

UA do indeed use the gold BP's as you describe (and you get the class printed in nice big letters across the top e.g. "INTERNATIONAL FIRST CLASS"). They used to give out silver/gold ticket wallets to J/F passengers as well. All of that is supposed to be getting replaced by white thermal paper (yes, paper) bearing bar codes for scanning at the gate, with many self service machines already dispensing this.

As long as BA stop short of using till receipts, I'm happy with the single design for BP's.