This is an old, traditional marker rendering technique and is similar to Tip-to-Tip blending. Create a palette with a variety of colours by scribbling onto a non-porous surface, such as acetate film.
Take a few dark or intense colours (colours ending in 5 or above work best) and make small dabs on your plastic palette. Lay down a generous amount of ink because it will be used up quickly.
With a lighter marker (colours ending in a 0 or 1 work best), pick up a spot of dark ink from the plastic and colour onto your image. This is great for small spots of blended colours. If you want a colour to blend to white, use the colourless blender to pick up colour from your pallet.
For larger areas, keep picking up colour and feathering it into your work in the same direction as the first stroke.
Always remember to scribble off the darker colour onto some scrap paper to keep your light marker tips nice and clean.