post values to custom post type which has advanced custom fields

If the custom field’s name (i.e. meta key) is correct and the field is enabled for the REST API, then you should be able to update the meta by adding it in the meta property, which is an array of meta key-value pairs, like so:

var newColor = {
  'title': $( '.title' ).val(),
  'meta': {
    'color': $( '.color' ).val(),
    'key2': 'value',
    'key3': 'value',
    // ...
  },
  'status': 'private'
}

Update: You can use register_meta() or register_post_meta() to enable the meta for the REST API: (without using any 3rd-party plugin)

// First parameter is the post type.
register_post_meta( 'color', 'color', [
    'single'       => true,
    'show_in_rest' => true,
    // Other args, if any.
] );

Update 2: Regarding the “ACF to REST” plugin, you should check the documentation here, but from what I could tell:

1. You’d want to enable the filters here.

2. Use the endpoint /wp-json/acf/v3/color to add or update your color custom post.

3. Use the fields property instead of meta for the default endpoint (/wp-json/wp/v2/color). So for example, you’d use 'fields': { 'color': $( '.color' ).val() } in your JS.

(You’re supposed to find that on your own.. but anyway, I hope it helps and please check the docs for further assistance.)