If I use one single quotation mark (') in a code block. The color of following sentences becomes weired.
Please see the attached image: in case 1, this line "The color is correct" is green, while in case 2, this line "The color changed" is red.
The only difference is that I use (Didnt) in case 1 but use (Didn't) in case 2.
This occurs in both ver. 1.5.11 and ver. 1.5.14, on windows 10.
This is an upstream bug with CodeMirror which is the editor that Joplin uses. It seems to be a specific edge case when rendering bash within markdown documents. You'll have to file an issue with them to get this fixed.
For now you can put a backslash (\) in front of the single quotation to tell the editor not to highlight it.