Line Chart Showing What I Think Is Progress

[HarryGreenwood]

Hi,

I have a line chart which I didn't produce but am I trying to understand.

Please see the attached file to see the chart.

My query is, why is the first part of the line blue? I'm hoping its showing progress driven by a date but not sure how that works.

If it isn't showing progress, then how would I make it so it did?

Thanks.