Matrix Grid lines Custom Colors

prakash11440278 , one way is to choose style under the style.

or See if you can create one for your need using the theme

https://powerbi.tips/tools/report-theme-generator-v3/

Another option is conditional for that will only work for values and you have to do for all columns.

You can create a color measure and field value option

A color measure like

Switch(
not(isfiltered(Table[Region])) && not(isfiltered(Table[City])) , "Gold",
(isfiltered(Table[Region])) && not(isfiltered(Table[City])) , "grey",
"Blue"
)

Refer for steps

https://radacad.com/dax-and-conditional-formatting-better-together-find-the-biggest-and-smallest-numbers-in-the-column
https://docs.microsoft.com/en-us/power-bi/desktop-conditional-table-formatting#color-by-color-values

For isinscope, isfiltered

https://www.kasperonbi.com/use-isinscope-to-get-the-right-hierarchy-level-in-dax/

https://powerpivotpro.com/2013/03/hasonevalue-vs-isfiltered-vs-hasonefilter/