Clue: Grey Geneva, maybe, lacking a leader? It's a Swiss hallmark (10)
Answer: NEUTRALITY
Explanation: Definition: It's a Swiss hallmark
 NEUTRAL(of a pale grey colour, as in "walls of a neutral shade") + "city"(an example of which/maybe is Geneva, Switzerland) **minus ****its 1st letter**(lacking a leader).
Defn: …, one of not taking sides in a conflict.