style.configure('My.Horizontal.TScrollbar', troughcolor='red')
hs = Scrollbar(app, orient='horizontal', style='My.Horizontal.TScrollbar')
hs.place(x=5, y=5, width=150)
hs.set(0.2, 0.3)
app.mainloop()
if __name__ == '__main__':
    main()
Changing the appearance of a Scrollbar in tkinter (using ttk styles)