Well, they won't technically
be Columbian Rocks, since those are more rare than Delawares. What you will find is a Delaware that has had Columbian Rock blood in the lines back when Delawares almost died out entirely as a breed, then the hatcheries didn't not cull heavily to get the type back.
Delawares have barred hackles, as do the hens. The roosters have barred tails, the hens have tail black (black feathers with white edging, and barred covert feathers).
With Columbian Rocks or improperly colored Delawares, the hackles will be more solid, like a Brahma, and the males may have solid black tail feathers.
I have not had Columbian Rocks, but here is a properly colored Delaware cockerel where you can clearly see the barred hackles and tail feathers:
Here is a Delaware pullet:
Yard full 'o Rocks has Columbian Rocks and has posted pictures of them here on BYC often.