hardy boy casefiles - Book Edge Color

[MikBoy]

Why do some books have yellow edges and some have white? If books are in the same condition which would be best to keep?

[SkyWarp]

I am not an expert on this, but I am guessing that since earlier printings had yellow edges, if you find a casefiles book 1-66 with white edges it was probably printed after #67 was first published. That is just my guess though. 

As far as which is worth more?  No idea. 

[tomswift2002]

The yellow pages ran from August 1986 to August 1992 across all the Files-Casefiles series.  The yellow is actually a dye and was held over from the paperbacks of the 1960's.  Cutting the dye cut production costs.