Retain same line colour when changing field parameter slice values

Hello Power Bi heroes,

I have an issue that needs help. See I have a line chart with two Y axis. The axis is displayed based on field parameter slicers created for each line (basically the same email metrics created from measures for both slicers).

But the issue is the default colour lines (dictated by my company's theme) is too similar. But when I try to change the colour of the line, it only changes for the current selected value and no the entire option in the series. 

So in this case, only 'total delivered' is changed to purple. Not the entire primary Y-axis line. And if 'total delivered' is selected on the secondary Y-axis, it's purple as well.

I hope I explained this well enough and hope I can get some help!