An Answer to your comments

FYI: Robert Culp was offered the part of Napoleon Solo, but turned it down. Robert Vaughan may have been the star of U.N.C.L.E., but David McCallum as Illya Kuryakin was more popular.

Robert Culp was an established actor. He was the "name" that Sheldon Leonard signed to his project I SPY. This is probably why he alone appears in the opening credit sequence. At that time, Cosby was a virtually unknown. He was the up-and-coming stand-up comic, but with little television exposure. However, his comic routine about karate caught the eye of Sheldon Leonard who though he might be the man he was looking for.

In interviews, Robert Culp has recalled his first meeting with Cosby.
They were brought together for a "read through" of the pilot script with Sheldon Leonard and the other producers. They each had the script to review. Cosby, not a trained actor, was giving it his best shot at the reading. This was also 1964 when black actors didnot have much exposure on television. In that pilot script there were several "racial" jokes(?).
But Cosby showed his contempt for them by flipping them around.
Culp was impressed with what Cosby had done and he told the producers,
"He just showed us what to do, this has got to be a 50-50 for it won't work."

There were only two racial references that I can recall which occurred in the first season. Cosby and Culp voiced their displeasure and insisted
no more racial stuff. As Cosby has said, "the audience can see that he is white and I am black. No more reference is needed."

Hope this is helpful.