Kommentar zu Bereschit 38:30

אשר על ידו השני THAT HAD THE SHINING RED THREAD UPON HIS HAND — The word יד is written here four times corresponding to the four acts of sacrilege which Achan, who was a descendant of Perez, committed with his hand. Others say these correspond to the four things which he took with his hand of the spoil of Jericho: a Babylon garment, two hundred shekels, and a wedge of gold (Genesis Rabbah 85:14).

זרח. On account of the woolen thread which was red in colour. The word זרח basically means red, such as the colour of the sun at the time it rises and when it sets. If it does not appear red during the day this is because of the excess amount of light during those hours making it impossible for us to notice the red colour behind all that light. We find confirmation of the redness of the sun in Kings II 3,22 when the Moabites were deceived by believing that the rising sun’s redness represented blood remaining from a violent battle and they thought they could then simply move over to the camp of the Israelites and pick up the spoils.

זרח, she named him in commemoration of the red string she had wound around his hand. This colour symbolises a warning.