It's very simple:
Vases like this, with the clay unglazed on the outside, are fashionable and lend themselves very well to decorating with colour pencils. If the vase already has an attractive relief pattern, then all you need to is follow your colour instinct, or match the colours of your tablecloth or tea service – or choose your girlfriend’s favourite colour if you’re making an original present for her.
Take the Art GRIP Aquarelle pencils in your chosen colours, and colour in so that neighbouring areas are in different shades. After that, you can make the colours mingle in a beautiful way by working over them with a damp paintbrush. If the surface is very absorbent you’ll need to wet the brush rather more. We recommend coating the finished vase with clear varnish. Then the design will shrug off the inevitable drops of water, even over a long period of use.
Be brave: experiment! There are many possible variants. For example, different colours, but preferably matching shades. We coloured only part of the design, but perhaps you prefer to colour the entire vase – then you may need to plan your colour scheme carefully!