Drybrushing is a great way to get additional texture and color while at the same time leaving a bit of your collage obscured.
Begin by dipping a dry brush into paint. In this photo a small brush and small strokes are used. The brush is tapped onto the surface, adding paint in a stippling manner rather than linear.
To achieve a more linear and consistent look, a dry brush was loaded with paint and then moved across the surface in a linear manner, creating a uniform shade.