Have the letter next to the person you are pming back and forth with change color when you reply to a pm.

Instead of having all of the letters be the dark and light gray (for my selected style ofc) all the time, have it change color when you reply to the pm.

For example:

Not rly needed. When you reply to pm u get this symbol >>.
Its good how it is

Voted no

Oh wow, never noticed the >>.