Sakura Koi Coloring Brush Pens contain dye-based ink and can be used to add vibrant color to any sketch, journal, cartoon, illustration, or rubber stamp. Make fine, medium, or bold brush strokes just by changing the amount of pressure to the nib. The durable tip will quickly spring back to its original shape. Odorless, water-based solvent facilitates smooth blending and layering of colors. Dark Cool Gray.