Using QGIS 3.4.0, I have created a new custom color ramp, using:
Settings > Style Manager > Color ramp > green plus sign
I saved the new color ramp as follows:
The color ramp works just fine.
Out of curiosity, I searched the entire local drive for the new ramp, using the text string (test_example). Nothing returned.
So, where are these new ramps stored, i.e. folder and file name?