My blue marks didn't come out at all. I bought a redwork panel printed in blue. Had to do the whole thing in blue embroidery.
pre-printed embroidery panels / blocks are generally printed (permanent) so they do not fade away before you get them stitched- the (companies) assume your embroidery threads will cover the marks. a blue soluble marker is made to wash away. often they disappear when your quilt is laundered- if you have a problem with them I would contact the company (brand of marker) and ask them- they have the tips/hints/helps for their specific product. I have found over the years all 'blue water soluble markers' are not created equal.