A]  Dip the tip of a blender pen on to the corner of a Stampin' Pastel, then apply to the stamped image.
OR  
B]  Brush the tip of a blender pen, Aqua Painter, or wet watercolour brush directly on the tip of a Watercolor Wonder Crayon, then apply colour to the stamped image. 
OR
C]  Outline a section of the stamped image with a watercolour pencil, then use a wet watercolour brush, Aqua Painter, or blender pen to pull colour where desired.
OR
D]  Press the closed lid of a Classic Stampin' Pad down against the ink pad, creating a small pool of colour in the lid; then open the lid. Use a damp watercolour brush or Aqua Painter to lift the ink from the lid and apply. 

QUICK TIP
For more saturated colours, watercolour with Classic ink refills.