Sceloporus malachiticus has a length of 12 - 19 cm including the tail.
The tail is relatively short, covering about half of the total body length.
The body color is emerald green, but at lower temperatures the animals turn darker to brown to almost black.
The lizard is active during the day and is a typical arboreal dweller.
Sceloporus malachiticus is often found sunning on walls and posts and stands out because of its green color.

Twan Leenders, an accomplished herpetologist and author of the Guide to the Amphibians and Reptiles of Costa Rica (and some other books on reptiles and amphibians in Costa Rica), helped me identifying this species.
I met Twan during my visit to the Biological Station Rara Avis (now an Eco Lodge) in the Braulio Carrillo National Park in Costa Rica in 2003 and ever since I sometimes ask his assistance in identifying reptiles and amphibians that I have seen that I have seen but not been able to 100% identify.

Finca El Pilar, Antigua, Guatemala, 16 January 2020