This lovely drawing features a young girl enjoying a walk in the rain with her umbrella. Her expression is one of delight, and her brightly-coloured rubber boots are a perfect contrast to the grey day. To add to the peaceful mood, a cozy cottage is visible in the background, inviting one to get out of the rain.
If I were to colour this drawing, I would use a muted palette, with lots of neutral colours to capture the mood of the rainy day. For the girl, her coat would be a mixture of blues, greys and maybe a dark mustard yellow. Her umbrella can be a deep pink or red colour, to make her stand out in the grey setting. The sky would be a deep, muted blue, with some white clouds scattered throughout and a hint of emerald green around the cottage in the background to give it a peaceful feeling. Finishing it off, I would use a soft, warm grey for the ground to bring everything together.