There are many factors affecting the shear strength of rock masses. The shear resistance of discontinuities could probably be regarded as the most critical factor in this respect. As the roughness characteristics of discontinuity surfaces have a great influence on the shear behaviour of discontinuity, it is of primary importance to study the roughness characteristics of discontinuity surfaces. The shear resistance of a discontinuity is a function of the amount of friction created due to contact between two surfaces during shear displacement. Therefore, it is also necessary to analyse the contact characteristics, called the matching degree, together with the roughness properties of discontinuities. The effect of the degree of surface matching on the shear characteristics of a discontinuity has not yet been fully described. In this paper, the aim is to determine the degree of matching of surfaces under different normal loads and state its significance in the shear behaviour of discontinuities. In order to visualise the effect of the degree of matching, both surfaces were dyed with a low absorbable paint in the form of a thin film. The shear strength of discontinuities at different normal loads was determined and photographs of the surfaces were taken using a digital camera with 1600x1200 pixel resolution. The photographs were analysed on the basis of colour difference. Thus, the parts of the surface where the paint was eroded due to friction could be identified and analysed. This made it possible to isolate the effect of the degree of surface matching together with the discontinuity surface roughness characteristics.