I don't think this is in the bundled edition of TeeChart.
I achieve this by creating an additional line on the chart and then making points on the line of the background colour along the y = bottom axis and then, where the vertical line should be add a point on the bottom axis of the colour you want the line to be and then add the next point on the y = top axis with the same colour (and same x value) and then any subsequent points go back to the background colour.