There was indeed often a colored stripe at the top of the card. At computer centers I used, this stripe was used to indicate what JCL (job control language) s

There was indeed often a colored stripe at the top of the card. At computer centers I used, this stripe was used to indicate what JCL (job control language) statement was on the card. So the computer center would have a big stack of pink cards already punched with the statement to invoke the FORTRAN compiler, for example. The teacher told you to put a pink card at the front of your FORTRAN deck before you submitted it, or it wouldn't work.