Your answer, "The Ishmaelites", is not correct.
The correct answer to
Who sold Joseph (of the coat of many colors) into captivity?
is
The Midianites
as shown by
Genesis 37:36
which is
- KJV
- And the Midianites sold him into Egypt unto Potiphar, an officer of Pharaoh's, and captain of the guard.
- NIV
- Meanwhile, the Midianites {Samaritan Pentateuch, Septuagint, Vulgate and Syriac (see also verse 28); Masoretic Text Medanites} sold Joseph in Egypt to Potiphar, one of Pharaoh's officials, the captain of the guard.