FWIW, This happens almost every year on my Heliopsis. Usually later in the season. They don't seem to do much harm but they do really annoy me. They have never appeared on my Heliopsis that have dark stems!
This spring they clustered on my Lorainne Sunshine Heliopsis. I was frustrated since it was early in the season. So because of them, AND because the plant reseeds so much to the point of becoming invasive, I ripped the whole thing out.
So far, the red aphids have not arrived to party on my other green stemmed Heliopsis. And as always not on my dark stemmed Heliopsis.
Sorry, I cannot remember the varieties of Heliopsis I have. I went crazy on them one year and got several varieties. Lorainne is easy to remember since she is variegated.
Not sure any of this info helps you. But that's my experience
