I have several types of buddleia. In my garden, I don't think it's the color that matters, it's mostly the location of the plant.

The 3 buddleia under my tree get less action, whereas the 3 near the street are always visited.

Butterfly visitation to nectar sources is dependent on a lot of factors. Time of day, amount of sunlight, nectar production, and even experience. However, there was a study done on this very subject (Relationship of Butterfly Visitation with Nectar Qualities and Flower Color in Butterfly Bush, Buddleia Davidii. Joseph D. Culin, Department of Entomology, Clemson University). It's just better if I quote the conclusion;

"In butterfly bush, butterfly visitation appears to be based on both flower color and nectar qualities. In general, visitation rates were greatest in those varieties that produced the most nectar, and those having nectar containing relatively high amounts of sucrose in relation to glucose and fructose. However, of those varieties, visitation rates were low on those having white or pale lavender flowers and greatest on those having red, pink, or lavender-pink flowers. This is probably due to the fact that butterflies, unlike many insects, can perceive red wavelength colors. Although many white flowers have been found to reflect ultraviolet (UV), which is highly attractive to many insects, preliminary UV analyses have indicated that butterfly bush flowers do not."

Hope that is helpful,
Elisabeth

Right now i have "white profusion"," pink delight" and "purple knight". I really don't notice a preference.
I do find that when one of them has alot of blooms that they prefer it over the one with little blooms. But that would be a natural reaction I would think. i have recently added nanho blue and another pink one, but only because they nursery was closing and I paid $3.00 a piece for them. They will probably bloom this spring. I will observe them then. Butterflutter

I also think that location, location, etc. is very important. But I do notice that the 'Cornwall Blues seem to get the most attention in my yard while the Nanho Purple seems to get the least. I have probably more than 10 and maybe 15 buddleias in my tiny yard and lantanas all over the place but the most activity seems to be around the Cornwalls. This year I am adding a bunch of the small compact varieties so it will fun to see how they draw visitors.

I also find that sometimes the species of butterflies may be partial to nectar sources they like over others. I have noticed that the hairstreaks like the curassavica flowers over the buddleias. And female monarchs use my milkweed blooms more than the males.

One day I went out to see what was going on in the garden and it was at a time when there were blooms all over the place. But I saw only one butterfly and it was feeding from a single dandylion flower on the edge of the driveway. It was so frustrating to see after all my work in preparing an absolute banquet for the ingrates. Murray