The mc OneDark theme comes in two flavors, an 8/16 color option (onedark.ini) and a 16M color option (onedark16M.ini). The 8/16 color version is entirely dependent on having installed the relevant OneDark theme for your terminal too as it uses the color palette fixed by your terminal.

See Konsole color scheme for example.

The 16M color version can be used independently of any terminal color scheme, but requires true color support in the terminal.

Installation

Copy files from ./skins to ~/.local/share/mc/skins
Copy files from ./config to ~/.config/mc/ (optional)

Activating theme

Option 1: edit ~/.config/mc/ini and add skin=onedark:
sed -i 's|$^skin=$.*$|\1onedark|' ~/.config/mc/ini

Option 2: choose the skin through the mc UI with:
F9 > Options > Appearance

Option 3: run mc with specific skin:
mc -S onedark

Option 4: add export MC_SKIN=onedark to the initialization file of your shell (e.g., ~/.bashrc or ~/.zshrc):
echo "export MC_SKIN=onedark" >> ~/.zshrc