Better contrast, maybe a border if possible

[MuhammadSawalhy]

This is annoying to eyes to see colors with low contrast between them, there are lots of suggestion to fix this issue, such as using foreground and background in the virtual text, or adding a border to the color small square if possible:

[RRethy]

There are many highlighters already (see :h g:Hexokinase_highlighters) and you can define your own custom highlighters (see :h hexokinase-custom-highlighters and https://github.com/RRethy/vim-hexokinase/blob/master/autoload/hexokinase/highlighters/virtual.vim). I'm not pushing new features to this plugin, only bug fixes.

I'm going to leave this issue open and I'm open to PRs, but I probably won't implement this.