If a variable id begins with an uppercase letter and goes on with lowercase letters, only the uppercase letter is highlighted.
Possible workaround : try to match pasp--atom after pasp--variable:
(setq pasp-highlighting
(list
pasp--constructs
pasp--constant
pasp--variable2
pasp--variable
pasp--atom))
Note : I wonder if this issue has been introduced by my workaround on issue #2