Would second earlier poster's tip of using laundry marker to colour-in light polyester stitching that will not dye. I've also used indelible felt-tip markers for this, on blue as well as black garments. You need a fairly steady hand, but it works...
Dylon is very good for standard colours. For a wider range of shades, I've also used Procion dyes www.kemtex.co.uk/procionmxdyes.html - they can also be used in a washing machine, but need washing soda plus salt to fix them. The suppliers in the link above have a leaflet with details of method. Easy to use.
It's good advice to wear rubber gloves, whatever brand of dye you use.