Different sources are not highlighted in different colors. Instead, orange highlighting is used for partial matches, red for full matches. Clicking on a highlighted sentence shows you the matching source text, with another percentage indicating how similar your sentence was to the source.
Unicheck was able to fully match some plagiarized passages with their source texts, unlike most free tools. However, the percentages it detected overall (44%) were comparable to those of Check Plagiarism.
Pre Post SEO did find the occasional full match, but in most cases it was only able to find partial matches, like most free checkers. Even with unedited texts, this checker performed relatively poorly. Its overall average was 29%. 2b1af7f3a8