I would consider this a bug in swagger, but I have seen problems in other editors e.g. when highlighting YAML.
When a string scalar is surrounded by single quotes '....' the only escaping within that string that can be done is inserting a double single quote to indicate a single quote:
'It''s a good question'
When double quotes, "....", go around a scalar string you use backslash (\) for escaping, and you have to escape at least the backslash and the double quotes. In addition you can escape other special characters like linefeed (\n) and escape an end-of-line by preceding it by a backslash.
The YAML spec says there is no way to escape characters inside literal scalars ( starting with |), so you cannot insert extra newlines, or other escape sequences withing these.
For the folded style (>), the escaping behaviour is as with literal scalars.
All string scalars except for plain scalars (those without any quotes or >/|) can contain : followed by space without problem, and if an editor interprets that differently, that is understandable (as full YAML parsing is expensive), but incorrect.