Select Keynote Field for Legend

[Libbya]

I have a custom block that includes a sheet keynote field.  When trying to setup a keynote legend for those keys, they are 'filtered out'.  Why?  Any ideas on how to get the legend to accept keynote fields that are not generated by the stock keynote tools?

[Libbya]

I guess what I'm really asking is...  What makes a key?  In other words what is it that makes an item so that it is recognized by the keynote legend for scheduling?   I assumed that it was the keynote field but that does not make it recognized by the legend.