The one at upper right is the only one that has "Casino Hotel" inside the oval on the front of the matchbook. All others say "Hotel". Note the changes in the Los Angeles telephone exchanges; I don't know whether they actually had physical offices in LA or whether these are "foreign exchange" numbers that were local to dial from LA but actually rang in Las Vegas. This was before the 800 number system and when it actually cost more to dial "long distance" (or maybe say "operator, give me long distance") .

I have the one you show but no others with pink insides. I doubt this is due to fading, but I guess it could be a color misprint. Sure is hard to read 50 years later!