The greenish blue is in a subfamily of small butterflies (Polyommatinae) that are known for their eye-catching blue colors on their upper side — the aptly named blues. Males of this species are generally greenish to grayish bluish above, while the females are dark brown above. They are very active, flying just above the ground, mainly in June and July in clover-strewn wet meadows and forest openings. Being low flyers, they like to visit low flowering plants for nectar (like the clover in the picture). Caterpillars feed on clovers. Males like to join “puddle parties,” sipping up salts and nutrients. In Montana, these butterflies are reported across the state. 
Photo by Glenn Marangelo on 6/22/20 in Condon, MT.