FOR MAC SCREENWRITER 6.7 (or higher) USERS:
If you see blue or colored text in a PDF version of a Screenwriter document where strikethrough or strikeout styling is supposed to be, the solution is pretty simple: Apple did not have the "built-in" ability to do strikethrough in MacOS 10.15 (Catalina) and 11.0 (Big Sur). They added it as of 12.0 (Monterey).
If you upgrade to Monterey or Ventura you will be able to see strikethrough formatting. Strikethrough is used a lot in comparing documents in Screenwriter to show material that has been deleted between the document versions.
The blue color is due to an older preference default, which is now red -- but you can change it to whatever you want in Screenwriter's Misc. Preference panel:
Note that if you loaded the same script into Screenwriter 6.5 on Mojave or earlier, you would also see it properly shown as strikethrough.