Want two-level highlighting of strings

I’d like to highlight strings with two colours, dim and bright. (May I show bright in bold, dim in normal?) Dim should be:

1. Quotes, prefixes, suffixes, delimiters: R"QQQ("alpha")QQQ"sv
2. Special characters that have special meaning. "alpha \n bravo \u00A0 charlie", "\n" (well, the latter is entirely dim)
3. Backslashes only if they escape slashed character. (I cannot format this with Markdown — in "\"" only the middle quote should be bright)