Given that this was posted in the "Northern Gardening" section, it is unlikely that osmanthus would be able to survive in your zone.

Lily of the Valley, or lavender (down to zone 5, not sure if it will survive for you) could also possibly complement lilac. Hyacinth and honeysuckle (down to zone 4) might be possibilities. Fragrant lavender color rose varieties. It's not fragrant but there are some varieties of "hardy hibiscus" that are the same color as lilac. Garden phlox.

Common milkweed can be fairly fragrant and survive down to zone 3.

In terms of color, maybe something like veronica bush or beebalm.