Selina, I have made sea glass and it is fun! Here is a tutorial, I hope it helps: https://www.hometalk.com/41958355/transform-plain-glass-vases-into-gorgeous-sea-glass
You can buy sea glass look spray paint in lots of colors! Easy peasy. :)
Add coloring to school glue (like Elmers) and paint it on the glass is the easiest way.