It won't be a very long posting... I thought I'll add some nice and easy screencaps so there are at least ten pics ;-)
It is scarcely anything mentioned in I Spy - but it's a 60s series, so I wasn't astonished looking at those few pics.
lamardeuse was the first who posted this scene and she wrote "Kelly's coat may be the gayest thing ever." ("Cops and Robbers")
Kelly was flirting with a nice young woman as Scotty called for him and pointed to a man who was carrying a weapon. Kelly looked at the man, he probably thought of the young woman and said: "He is not my type." ("Affair in T'Sien Cha")
The man wants to kill Kelly as suddenly some people are coming round the corner. Kelly knows the bad guy can't do anything because of the witnesses and he tells the man: "Come on, go ahead. Shoot me, sweetheart." ("Lisa")
The photographer is a bad guy too and he tells Kelly: "Kelly baby you look sharp." ("Always say Goodbye")
I think it's a pure accident and it wasn't planned by the director of the episode. They were often filming in public, and this time two young women were going along the street handholding.
Robert Culp seems to be very interested ;-)
This woman is a really bad guy and she shoots her fiance because she thinks he betrayed her. I think her touching the woman (twice) probably is a part of the script. ("Dragon's Teeth")
Now it starts to get interesting. This man is a tailer (his shop is called "Lee Pink") and Scotty and Kelly ask him about a woman they are looking for. His answer: "My name is not Lee Pink, it's Leon Pinkus. I haven't seen any girl."
He acts soft and sounds apologizing as he speaks - someone who would have been called "fairy" back then, I think.
Kelly seems to be a bit disgusted as they leave the room. ("No Exchange on damaged Merchandise")
These two women seem to be characterized as a couple in the script, with an obvious distribution of roles.
The right one plays a "man", with shorter hair, wearing trousers and acting the part of a leading role. The left one has longer hair, she wears skirts and does what her girl friend tells her. ("Apollo")
And now the one and only reaction of Kelly I found to homosexuality.
He doesn't know his own people are talking about a female major. He is outraged and asks: "You want me to cultivate a romantic interest in a major?"
Scotty keeps a very straight face as Kelly is asking. Well... "Straight" was what Kelly seems to show us in the scene. ("A Gift from Alexander")