1)
Who wear Techeles?
1.
Radak: The officers who came with Melech Ashur.
2)
Why does the verse mention Bachurei Chemed riding on horses?
1.
Radak: When [Shomron] saw them in nice garments, riding on horses, it desired them, and mixed with them and learned from their deeds.
2.
Malbim: [Shomron] desired Bnei Ashur due to their beautiful Techeles garments, and their level (they were officers), the beauty of Bachurei Chemed, and their Gevurah ? they were cavalry riding on horses.