Er,

this might be a cool photo of the datura blossom and the mystery insect within, but it's a miserable thing to ID anything by. Still, I gave it a try and came up with Dicyphus as a possibility. At the time this was observed there were four datura flowers open, and each one had at least one of these inside. These are similar, but unlike other mirids commonly found in the yard: greener, longer body, distinct neck and head shape, bulging vental abdomen to name a few differences. Here are some much better pictures of some bugs positively identified as that, showing similarity in body shape, head shape, eye placement and coloration to my bugs.

Genus dicyphus is in the large and wonderful mirid bug family. Unlike most mirids they are carnivorous, feeding on pests such as whiteflies and mites, making them a welcome addition to the garden fauna. Maybe my bugs wait inside the flowers for unwitting prey to drop in. If I can see them feeding, that would probably confirm this tentative ID. And I wonder where they go when no datura are open?