Changing the sort icon in a datagrid

[Glen Bojsza]

Hello,

I was hoping someone can tell me how to change the Icon Image used by the
datagrid sortarrow button.

I have modified the colors of the datagrid to adhere to a theme for the
project and the current icon image is too dark to be noticed so I want to
replace it with one in the standard library or an image of my own.

thanks,

Glen