Conditional Format Bars and Line in a combo chart by year

Thanks for the reply from PhilipTreacy , please allow me to provide another insight: 
Hi  MWC914 ,

I created some data:

As far as I know, Line Chart and Clustered Column Chart doesn't support customizing the color of Line y-axis, this is due to the design of Power BI, you can use the following method instead: multiple measures are created, and each measure only displays the data corresponding to the year, otherwise it is empty.

Here are the steps you can follow：

1. Create measure.

2023year =
var _mindate=MINX(FILTER(ALL('Table'),YEAR('Table'[Date])=2023),[Date])-1
var _maxdate=MAXX(FILTER(ALL('Table'),YEAR('Table'[Date])=2023),[Date])
return
IF(
    MAX('Table'[Date])>=_mindate&&MAX('Table'[Date])<=_maxdate,SUM('Table'[VALUE2]),BLANK())

2024year =
var _mindate=MINX(FILTER(ALL('Table'),YEAR('Table'[Date])=2024),[Date])-1
var _maxdate=MAXX(FILTER(ALL('Table'),YEAR('Table'[Date])=2024),[Date])
return
IF(
    MAX('Table'[Date])>=_mindate&&MAX('Table'[Date])<=_maxdate,SUM('Table'[VALUE2]),BLANK())

2. Lines - Apply settings to (select specified measure name) - Color (set different color).

3. Result:

Best Regards,

Liu Yang

If this post helps, then please consider Accept it as the solution to help the other members find it more quickly