Recolor the whole vector icon or parts of it. Solid color fill or gradient.
Fill the background of the icon with a solid color or gradient.
Stroke the icon, choose a stroke color and a thickness.
Place the text on the icon, select the font, size and position.
A small addition to the icon like plus, minus, warning mark, etc.
The spacing from the vector icon to the borders of the viewport.
Upload icons and create font files (WOFF, WOFF2, TTF, EOT).
Reduce icon file size.