Draw your fashion illustration with a black or gray water soluble colored pencil in an artist's sketch book or on a piece of watercolor paper. Such paper is heavier than regular notebook or copier paper and can absorb small amounts of water without damage.
Add color to your illustration. Use other colors in your water soluble colored pencil set and add design details to garments and fashion accessories illustrated in the drawing. Fill in shapes with broad and narrow watercolor pencil strokes to give depth to your illustration.
Dip your watercolor paintbrush in cold water and use the brush tip to blend colors. You can also use your watercolor brush to remove dark sketch outlines for a professional-looking illustration. To remove heavy dark outlines, wet the lines with your watercolor brush and dab your illustration gently with a clean, moist paper towel to remove loosened dark sketch marks from the paper.