Hi Loretta,
Millenium is a great-looking ornamental onion. It has some serious plant breeding behind it, and they charge for it. Millenium has a nice Lavender color that would, as you say, contrast well with yellow. Actually, I think ornamental onions are available in several colors. So far the only similar zinnia blooms I have seen have been in light colors. Some of my "onion-flowered" zinnias have had fairly large blooms. Zinnias are capable of near-spherical and almost perfectly spherical blooms, so they can compete with Alliums in that regard.
I think it would be possible to do a lot of cross-pollination and get a complete range of zinnia colors into "onion-flowered" zinnias. They might be useful ornamentals. That is something for me to think about. But I might be, as the old saying goes,
getting too many irons in the fire.
ZM
