The Wada index based on the weighted and truncated Shannon entropy is presented in this paper. The proposed Wada index can detect if a given basin boundary is a Wada boundary. Moreover, the Wada index does represent the number and the distribution of different colors (attractors) in the two-dimensional phase space of initial conditions. The Wada index is based on the standard box counting algorithm, but computations in each box are based on the weighted and truncated Shannon entropy. That makes the algorithm for the computation of the Wada index conveniently applicable for different basins of attraction represented as color digital images. Computational experiments are used to demonstrate the advantages of the proposed index and compare it with other existing techniques and algorithms for the numerical analysis of Wada boundaries.