Solvents break down and dissolve the binder in the colored pencil lead and can create a smooth painterly like surface. It is similar to watercolor painting, accept you are using a solvent instead of water to blend the colors with and to create various effects with the use of different application tools.
Solvents can release toxins into the air and those toxins can cause lightheadedness, breathing problems, memory loss, brain damage or even cancer. Even though a natural solvent's container might say it's natural and safe, not all "Natural" products are 100% safe, so be wary of prolonged exposure and usage. Citrus solvents contain citrus oil and d-limonene, which are some of the most toxic solvents out there and have been linked to cancer. There is no hundred percent safe solvent, however, there are some that are significantly safer than others.
Make sure you use gloves and use proper ventilation by opening the windows and/or use an exhaust fan to expel toxic vapors. Dispose of any rags properly. Also make sure you undestand and know how to properly store and safely handle all solvents.
Keep on Creating!