Hi there,
this article explains how to change your default customizer colors.
https://docs.generatepress.com/article/generate_default_color_palettes/
And WP provides this filter to set colors in the Block Editor:
add_action( 'after_setup_theme', function() {
add_theme_support(
'editor-color-palette',
array(
array(
'name' => __( 'Scuro', 'castiglioni' ),
'slug' => 'dark',
'color' => '#382c33',
),
array(
'name' => __( 'Chiaro', 'castiglioni' ),
'slug' => 'light',
'color' => '#eeeeee',
),
)
);
}, 50 );