Highlight slicer/filter when in use

HI Anonymous ,

>>is there an easy way to change the colour of a (header of a) slicer when it´s in use? 

Current power bi not support do conditional formatting on slicer visual and cusotm visual header.

If you mean use slicer to formatting other visuals(table, matrix), you need to confirm slicer not have relationship to source table, then you can write a measure to compare selected value and current row content to return color code.
After these steps, you can enable conditional formatting on your value fields based on above measure with conditional formatting 'field value' mode.

Conditional formatting in tables

If you are confused on coding formula, please share some sample data for test.

Regards,

Xiaoxin Sheng