Keep line chart colours for rolling legend values

Hi all,

I've searched through the forums but can't find a similar question to this. I have a line chart charting daily performance over the past three weeks - using a relative weeknumber filter to update the chart automatically as we roll forward into each new week.

I want the colour of the most recent week to be darkest, with the week before that lighter, and the week before that lighter still. The trouble is that once I set the legend colours for each Trading Week on the visual, this is fixed for that specific week rather than applying to the week's relative position in the chart.

For example, last week the most recent values showing were for WK36, so I formatted that to be dark blue. This week, WK37 is most recent, but the dark blue formatting has stayed attached to WK36:

Is there a way I can set up conditional filtering on this graph to apply a set colour to the most recent  value in the legend, at any given point?

Thanks,

Nick