CoO/mantra isn't exactly a danger sense. "Color of Observation: Haki", I believe, is an enhancement to observation i.e. perception that comes from the haki (or willpower/determination/conviction etc.) of the person that allows him/her to predict the mental state of the target(s). It's used mostly to predict what a person is thinking. We've seen it used as a radar by Enel to count how many people are still on Skypea as well as by Rayleigh to measure how many creatures on the island he trained Luffy on were stronger than Luffy, as well as where those creatures were. We also saw that Gan Fall had his house at a place far enough away from the Vearth that he was outside of Enel's mantra range to detect. We also saw that if the person being read using CoO were not thinking anything, then that person's actions cannot be predicted (Gomu Gomu no Baka: Chapter 281, page 13 & 14 and Gomu Gomu no Octopus Rampage: page 15 & 16 same chapter). CoO isn't like Sharingan or Byakugan in Naruto where you can see everything around you and predict what's going to happen. It can only predict living things by what's on their minds.
That said, the point I was making was that as Enel said in Chapter 278, page 2, his devil fruit gives him a bonus/enhancement that allows him to use CoO at an extended range that allows him to pinpoint anyone within his mantra range and use "God's Judgement" i.e.
El Thor on them. This is an ability only he has because of the relationship between his use of devil fruit and his use of mantra (something Kizaru cannot do). If Enel is outside of Kizaru's CoO range, he cannot "see" Enel's attack no matter how fast he is. The only counter-argument I can think of right now for this is just to say that El Thor takes a while to charge up and Kizaru can easily turn elemental when he sees the beam of light forming over him

. But if Kizaru doesn't physically see the attacks coming and prepare for them, Enel can attack him from outside of his CoO range and keep avoiding Kizaru because Kizaru will not know where Enel is attacking from.
That would be an interesting match up to see and I'm curious how Oda would play out such a battle since soru isn't exactly as fast as electricity and Lucci hasn't shown any signs of CoA haki. Anyways, it'd be nice if you could give some reference just for verification

.