{edit} added two previously discarded as poor-quality photos of the tail to show the white outer tail feathers to aid any IDs. The one bird I photographed and a second nearby were uniformly gray. No tan/pink or other earth tones to either bird. Underside was clean light gray fading to white all the way to the undertail coverts
Male flying south after copulation
third photo is the same individual. Seen on cultivated Lantana, but there is cultivated tropical milkweed within 10ft (not in bloom)
outside temp 100 F
In the light, the overall coloration was an even yellowish with a tint towards green. Thin lateral black lines on top of abdomen at/near hinges. Legs same yellowish hairy. Small black dashes or dots along sides of abdomen one per segment. Foliage was a honeysuckle bush for scale. Maybe 3/4 of an inch long. Always flew/hovered tail down.
(resubmit of accidentally deleted observation)