Using Inkscape (https://inkscape.org) to create symbols for markers in QGIS, and modify it in a text editor.
Extra:
You can assign "default" values to your parameters in the SVG.
For instance:
fill="#000000"
Will use black as fill color, unchangable.
If you want to be able to change the color, but have a default, then:
fill="param(fill) #EE0000"
This will use red as default, but you can change it in QGIS.
Learn Inkscape and Gimp: https://logosbynick.com/
Style Url (click, then copy url and import in QGIS): https://raw.githubusercontent.com/kla...