Actually, the best way to change this, and will keep this from being changed each time an update is done.
Login to the Admin Dashboard -> "Preferences" -> "Themes"
Click on the tab "Icons" and scroll down to the "Faveicon metas" section.
At the bottom of that listing are two lines with the color code. If you change those, then it will change and keep the new color code through future changes.
No need to manually edit files, or to have to keep changing them when you make site changes and updates.