“The OPRAN Magazine”, March 2013, page 153, had article witten Jenny Bailly “Color Magic”, where you may found the answer for your very actual question.
With regards, Miroslava,
There are several products and ways to make your hair look fuller. One of the easiest that I came across was at http://www.forhair.com/Articles/Hair_growth_vitamins_and_minerals.htm which is to dry your hair upside down with a hair dryer then flip it back over when you are done. Drying the roots first seems to help a lot.
You can find many other tips as well. If you cannot find a proper solution for your problem, I would recommend contacting a professional doctor.