Watercolour Pencils
Water colour pencils are very versatile you can just draw with them, wet the illustration after drawing to create more subtle blends, wet the end and take the wet pigment onto a watercolour brush to apply colour to your work. They come ain a huge variety of colour and so mixing becomes less of a chore. I occasionally use some white acrylic or gouache to pick up highlights and use them with traditional watercolours as well.