Based on your orientation for the front of the classroom, Green. Please note, that this is the "normal" orientation for rows -- which usually are considered to proceed horizontally (across) left to right -- as opposed to "columns" -- which usually are considered to proceed vertically (up & down) from the front.
Classroom orientations, however, often consider "rows" to be vertical formations, (that is, up & down from the front). If this is in fact the case, then the 4th row, 3rd seat will be Red.
- For Teachers