Allow importing existing hex colors

## Description

Currently on my projects I have hundreds of hex colors. I would like to systemize them and reduce their amount.

After importing the colors the Leonardo tool will be able to reduce the amount of the colors by combing colors into one with appropriate variants (100,200,300 etc.).

For example there can be no need to create a separate color entry per each imported items, there can be situation where a color is just a variant of the primary color. Probably for import Leonardo will need just a list of hex colors and then provide names on its own.

## Why do you need this feature?

That will help in using this tool for existing color schemes

The issue names no files, tests, or entry points. Begin by tracing how existing color schemes are created, then define the import input and expected color-merging and variant output; done means an existing list of hex colors can be imported and reduced into named variants.

Written by the indexing model from the issue text.