Hi,
I purchased Sublime for simple copywriting (‘prose’ as said in the advertisement), not code, and started to read the documentation and could customize the font and the size 
How are called the thin light yellow ‘bands’ on the left and how can I remove them?
That’s the incremental diff functionality showing you where you’ve made changes to the file; additions, removals and modifications. The colors used and the width of the markers are controlled by the color scheme.
The setting you want for that is mini_diff:
// Indicate modified lines in the gutter
// - true: Enables modified line indicators on all files
// - "auto": Enables modified line indicators on tracked files within Git
// - false: Disables modified line indicators
"mini_diff": true,
Many thanks for your help and the link. Much appreciated. I achieved to remove the incremental diff.