Here is a link to Sigil, which is an ebook editor. Another alternative is Calibre, which has fewer features, but is nice if you already use that tool for conversion and ebook management and don’t want to install anything further.
I simply compile as ePUB 3.0 in Scrivener 3 For Windows and upload it to Amazon KDP, and I get the random color issues in the TOC only now.
Yeah, that’s worth looking into why that is happening, but what you should be seeing is no text colour in the contents.xhtml file, nor the stylesheet.css file. It may be that when you pasted from Word some bad formatting came in, you should select the text of that file, right click on the selection, and use the Text Color ▸ Remove Color command.
So there’s no way to specify the colors of the TOC directly in Scrivener 3 For Windows?
You can change almost everything about an ebook. The whole thing is just HTML and CSS, which Scrivener provides extensive support for modification, and you can do an awful lot with just that. Here is a post that I’ve written on the matter.
But to reiterate, you really don’t want to be forcing hyperlink colours. Traditional bright blue looks terrible in dark mode readers—and for that same reason you don’t want black either.