Yes, you will. When the little seed containers are dry and starting to split, you should see hard black seeds peeking out. When 5 to 10% are as described, carefully cut the seed balls off and put them in a protected place to finish drying. When thoroughly dry, wearing gloves, rub them between your hands to free up the seeds. Separate out the chaff.
The problem is, you never know what you will get. They may be the same as the parent or may be a cross of the white and red or even of any other onion growing nearby.

Thanks for the info coho. I will give this a go.

I found that saving seed was fun and informative. More worth while would be to buy some open pollinated seed or onion starts. Two would be Stockton Red and Italian torpedo.
Plant the seed and grow your own transplants, or buy and plant the plants. Grow them and save some bulbs to replant when they sprout the tops. Grow only one type so they don't cross pollinate. The replanted bulbs will then bolt and sprout seed stalks (scape's). You should be able to save the seed for two seasons and have an unending supply of your own seed and onions. On the second year, save seed from a second type of onion. This way you can grow two varieties and never get cross pollination. Planting onion sets here is OK for green onions, but Crimson Forest and others make better green onions. Actually, Heritage Sweet
White Top-setters perpetuate them selves by producing their own little sets and might be more worthwhile and you can use the bulbs in the ground for cooking.

Hi coho,
When do you plant the seeds?
Lanabeth

Lanabeth,
I sent you an e-mail, but did not save a copy. Did you perchance delete it? Below applies to my zone.

If there is anyone growing onions in your area, they would be the ones to ask. That said, I plant my seed the 1st of September. You can plant directly into the row and thin or transplant the too close ones into another row. However, it is easier to manage if you plant into a small prepared place and then transplant into the permanent rows.
I transplant mine into the rows Nov 15 before the fall rain starts. The day before, if I can manage it.
Temps here are winter-20 t0 28F, and summer () to 110F.
This fall, I intend to plant seed somewhat earlier as my transplants are somewhat smaller than the ones Dixondale
farms sell.