This is where the php implode() function comes in handy. To be honest, I’m not exactly sure what your doing in your code, seems to be something missing that I need to put it all together. But here’s a short example:
if (have_rows('bike_color')) {
$colors = array();
while (have_rows('bike_color')) {
the_row();
$colors[] = get_sub_field('color');
}
echo implode(', ', $colors);
}