Juana is concerned and warns Kino that the trackers will be able to see his white clothing. So he takes off his white clothing
"....for dirty and ragged though they were they would show up against the dark night." (pg 83)
He did not really disguise himself -- he was naked. His own brown skin offered him better protection. When Juana looked for him,
"For a moment his body was black in the cave intrance, croughed and silent, and then he was gone." (pg 84)
He tied his knife onto a neck string so that he could have both hands free. As he made his way down the mountain, he shifted the knife to his back so that it wouldn't clash against the rocks and make a noise.
"Any sound that was not germane to the night would make them (the attackers) alert." (pg 84)
He knew he was not invisible, so he had to make sure that he did not send a stone rolling down the hill or make a noise.
"Kino's mouth was open so that even his breath would make no sound, for he knew he was not invisible." (pg 85)