Similar to the highlight feature, the underline feature comes with 1 pre-set color but 20 options to choose from:

Vitrium-Web-Viewer-Underlines-Options

Underline Sample

Vitrium-Web-Viewer-Text-Underline-Button
Vitrium-Web-Viewer-Underline-Sample

Strikeout Sample

Vitrium-Web-Viewer-Text-Strikeout-Button
Vitrium-Web-Viewer-Strikeout-Sample

Squiggly Sample

Vitrium-Web-Viewer-Text-Squiggly-button
Vitrium-Web-Viewer-Squiggly-Sample