You can use surface profile meter such as Accretech Surfcom-1400D profile meter. This method is suitable for all colored samples and measuring rang so high. Edge sharpness is been observed in the measuring system.
Dear Sir go with interference at air wedge experiment, introduce thin film between the two glass plate and allow the light to fall on it, you will get an interference pattern consisting of parallel lines by measuring their width you can find exact thickness. Just like newton ring pattern