CSS

change color accordion arrow bootstrap 5

.accordion-button::after {
    background-image: url("data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 16 16' fill='%23ffffff'><path fill-rule='evenodd' d='M1.646 4.646a.5.5 0 0 1 .708 0L8 10.293l5.646-5.647a.5.5 0 0 1 .708.708l-6 6a.5.5 0 0 1-.708 0l-6-6a.5.5 0 0 1 0-.708z'/></svg>") !important;
 }

Bootstrap default accordion arrow icon change

.accordion-button::after {
	background-image: url("path_to_image");
}
.accordion-button:not(.collapsed)::after {
	background-image: url("path_to_image");
}