One way to achieve this is creating dual axis.
If you put one line chart with tow colors, line is broken, BTW.
two_color_line_SM_10.3.twbx 27.2 KB
Just enhancing Shin's response, you can do this achieve the same result via adding a custom reference line as well
HTH 10.3 attached
two_color_line_v10.3.twbx 32.8 KB