I am using Arcgis 10.3. I can change the default color ramp by running the utility:
C:\Program Files (x86)\ArcGIS\Desktop10.3\Utilities\AdvancedArcMapSettings.exe
..and choosing an option from the ESRI.style
color ramp list.
Can I use a custom color ramp from, let's say, my custom.style
?
Did you try creating your own and following the instructions here?