Find unique values in two uncorrelated columns or sheets

[Jasonf450]

I have two columns (or 1 column in two sheets originally):

NamePass	NameMFA
user1	user2
user2	user3
user3
user4

I want to end up with unique values:

Result

user1

user4

Highlighting original unique values in original ColumnA (NamePass) is acceptable as well. 

Something like "If A not exists in B, highlight"

Ideas?  Thanks!

[#2]

@Jasonf450 

As variant

in D1

=FILTER(A2:A5,COUNTIF(B2:B5,A2:A5)=0)