We report an optical fiber experiment in which we investigate the interaction between an individual soliton and a dense soliton gas. We evidence a refraction phenomenon where the tracer soliton experiences an effective velocity change due to its interaction with the optical soliton gas. This interaction results in a significant spatial shift that is measured and compared with theoretical predictions obtained via the inverse scattering transform theory. The effective velocity change associated with the refraction phenomenon is found to be in good quantitative agreement with the results of the spectral kinetic theory of soliton gas. Our results validate the collision rate ansatz that plays a fundamental role in the kinetic theory of soliton gas and also is at the heart of generalized hydrodynamics of many-body integrable systems.