The top part of the window (attributes/objects lists) the following color notations are used:
red color - prohibited attribute / object for use in ENC (according to S-57 Appendix B.1) 
gray color - the attribute / object is deleted (not in use)

The bottom part of the window (attributes / objects descriptions) the following notations are used:
(!) - mandatory attribute
STRIKE - prohibited attribute (according to S-57 Appendix B.1 Annex A - Use of the Object Catalogue for ENC) 
(!?) - attribute is mandatory depending on the condition (it is possible to acquire with condition statement in tooltip)
(?)STRIKE - attribute is prohibited depending on the condition (it is possible to acquire with condition statement in tooltip)
green colored - added in version 3.1
gray colored - changes according to "S-57 Maintenance Document (Cumulative Number 5 - May 2000)"

In a table showing attribute values (right-bottom part of the window) it is possible to get symbols abbreviations terms used on paper charts by clicking mouse button over the INT-1 column.