I am not the best person to ask about coordinating jewelry as I don't always put the thought into it that many members do, with predictable results! It helps that I am lucky to be retired fairly young, mid-40s, so I can keep it casual. The butterflies also are actually pretty small and understated, so if you're not trying to build a set, they really go with anything.
In addition to the obvious pairings with RG pieces from just about any line, for me I have less white metal pieces (WG/Plat), and I think because of the diamond butterfly I can use them as a link to those pieces and the rest of my collection, which is mostly YG/RG. I think they also work with YG especially when the color is a bit softer and the necklace a bit longer like a MOP 20. I'm not sure how they'd look with a 20 in a bolder stone and prefer to pair mine bold ones, which are all YG, with YG earrings, although they'd probably look ok with the butterflies too. I think they'd be cute with the long sweet (16?) in RG, but don't have one to test it out.
I think it looks great with WG Chalcedony, which is the only WG I have but would probably look nice with other WG and, non-VCA, makes a great connection to some of my Tiffany Victoria. All of the pieces I have from that line are platinum and, even though I do wear them with other YG/RG VCA pieces since they're more diamond-y than metal-y, I think the butterflies are a nice bridge between those parts of my collection. I don't have and don't plan to get the matching ring, but I think it looks nice with any of the VCA WG flora rings. I would even wear it with Frivole BTF if I had or wanted it in WG. I don't have them, but am pondering a cosmos necklace, which I think would look great with the butterflies or, much cheaper, a lucky butterfly pendant in MOP, the one that sits level and is attached on both wings, not the little turquoise one, which I don't know actually if it comes in MOP.
Anyway, you can see I'm all over the place on matching. The truth is unless I'm going out for something special I usually don't try to coordinate jewelry that much at all and throw on what I feel like. I rarely think it looks terrible, although I can think of one recent time it definitely didn't work, and recently happily wore the butterflies to run some errands with iirc a crazy combo like BA magic pendant, solitaire pendant, YG JUC, YG Love, YG onyx 5 on one wrist, Tiffany ladybug, VCA ladybug, sweet heart, on the other. Luckily no ring! Just so you know where I'm coming from, I was also wearing colorful yoga pants, a long-sleeved black t, and fuzzy birkenstocks, so definitely not a style icon! Just doing what I felt like.