When you save & copy a requirement with mandatory fields and it can happen that the new requirement is missing the required data but still has a green tick next to the field . You will, however, not be able to save this new requirement due to the missing value.
If you have a Note Required on a transition, then the field label appears in red when the form displays. Adding the required note will not change the field colour to green , as it should.
In an older version of SBM, my form had a rule that said "if cost > 1,000, then make Needs Approval field required". When the form loaded, the "Needs Approval" field would ALWAYS be green . This is because the "Needs Approval" field will always be yes or no.