I think that the word "highlight" indicates what the function should do, however the pale yellow in the Evernote Windows app is barely visible, so it hardly highlights at all. The poor highlight contrast is especially apparent on web-clipped pages which may contain other coloured elements such as images.
I understand that some people prefer muted colours, whilst others (such as myself) prefer much brighter fluorescent colours for highlighting, so I would suggest that the solution would be to allow users to choose.
Many applications on many different platforms have a choice of highlight colours, either as a list of predefined colours (less useful), or a fully configurable colour chooser. Examples include;
Windows apps such as Word, Excel, LibreOffice Writer and even the minimalist Wordpad
Android apps such Excel and Google Docs.
Web-based apps such as Word Online, Gmail, Google Docs.
Evernote already has text colour selection. Couldn't a similar colour selection option be used for the Evernote highlighter?