Munsell Soil Charts are commonly used in archaeology to identify colors of soils and artifacts excavations. In situ, the procedure is done by visual mean and in a very subjective way, resulting in a time consuming and error-prone approach. To overcome these limits, an original application has been developed, ARCA: Automatic Recognition of Color for Archaeology. ARCA is a framework thought to be a valuable asset for archaeologists, since it may be objective, deterministic, and fast. In this framework, it is possible to convert RGB data to HVC color space. Users may import images in ARCA through a proper desktop application, which also allows operators to manually sample RGB data. Then, HVC notation is automatically estimated and provided to operator within an automatic generated filled report. ARCA moves from Munsell Charts but it has the advantage to provide an objective and affordable color specification system. In this study we present the results related to data acquired in controlled lightning environment with Color Assessment Cabinet on Munsell Soil Color Charts for trying to improve the lightness estimation. We focused on two color space conversions: RGB to HVC, and RGB to L* a* b* of CIELAB color space. Color coordinates are obtained through colorimetric measurements. We developed a method with three main phases and we computed transformation coefficients from observed and ground truth data. The color accuracy of our method is presented in terms of Godlove distance and through CIEDE1976, CIEDE2000, ΔL* , Δa* , and Δb* CIE metrics.