Hi Sam - I normally stick the colours in an array and return these from a php function, so it can go into both
add_theme_support('editor-color-palette', theme_colours());
and also the 'palettes' atrribute for the metabox color field.
Doing it like this is an ok hack, normally id just use the theme_colours() function to populate a select field though as that gives named colours e.g. 'Primary' => 'is-primary-color' and add the value/class to the html element