Right at the start of the book, we see that there are airplanes in the community, although we have no idea what they are for. One of their functions, apparently, must be to search for people.
What he did here was to use memories of snow and cold to make him and Gabe seem cold. By doing this, he was able to fool the infrared heat detectors that the search planes used to find people.
Jonas also uses the fact the he knows about color and the fact that he knows that the other people in the community do not know about it.
He use his imagination