refactor: move color extension to MD structure

[zkhCreator]

when my project with base framework with Color.init(light: lightColor, dark: darkColor), it shows conflict when I compile the project.

Move the functions into the struct to make the overall structure clearer and avoid potential conflicts

[cweider]

Is removal of public from the extensions a sufficient fix for your purposes? I’m fairly certain the answer is yes and, if so, it’s probable that #386 will merge alone. If not, this would be good to know – you’ll have uncovered another issue that needs addressing in addition to the public extension.

[cweider]

I’m noticing pervasive change of indentation from 2 to 4 spaces. For consistency (and in the interest of minimizing the change's size) the 2 space indent should be used.

Note: I’d not worry about rushing out a revision. If done, do it at your leisure. It may be some time before maintainers come through to give their review of the patch.