Esme spotted this male Mexican Sailor (Dynamine postverta mexicana) between several 88 butterflies all attracted to a muddy patch on a dirty road leading to San Marcos León.
The metallic light blue color above is only present in males of this species, the females have a strong white pattern on a dark brown background.
This butterfly photo is part of the blog entry The dirt road to San Marcos de León, which has more photos of this beautiful butterfly.