Custom Printed Pants
The drawstring is a detailing piece, so it does not go all the way around the elasticated waistband. It does go across the front couple of centimetres, and can be used for fine adjustments, but it is not intended to greatly alter the size of the garment.
You can create your custom design on both the front and back of the custom pants, and you can also print the left and right side differently if you would like - giving your four customisable areas (five if you opt for the label as well).
To an extent, yes. The drawstring will come in either black or white, and that is selected when you choose the top stitch thread colour within the design interface. You can see the colour of the drawstring changed on the preview as you select different options, so you can take a look at how your finished garment will appear.