I 'm not sure when exactly this comes up, but in the middle of working on the file, I suddenly get this huge RED code block. I can click on the 'R' and it changes my document (hard to say exactly what changed, there is no info on hover).
Bottom line: I don't like this! It's really hard to ignore and I do delete lines (and do NOT want to keep seeing them). But I'm not really sure if that's even what this is. Look at the screenshot and let me know if you have seen this and know how to get rid of it.
You are using Git in Dreamweaver and the thing troubling you is actually a feature. The section on tracking edits in Git on Adobe’s help page explains this. The colored bars on the left are called guttermarks:
A guttermark indicates those lines where changes have been made. Guttermarks in green indicate new code that has been added. Guttermark in yellow indicates modified code, while guttermark in red indicates a code line that has been deleted.
When you click the yellow guttermark, the application displays the change in the code. The deleted line of code appears in red while the newly added code appears in green.
Notice an R symbol at the left corner of the deleted lines of code. To add the deleted code back to your file, click the R symbol.
The Git settings in Dreamweaver have only options regarding your connection so it seems there is no easy way to make the guttermark effects more friendly to the eyes. But now you know what your dealing with and if you do not click guttermarks your eyes will be safe.