Solved by ptrblck in post #2 
              
              
                This code: 
File "/home/mona/research/code/expose/expose/utils/plot_utils.py", line 831, in __call__
    valid_mask = (color[3] > 0)[np.newaxis]

expects color to have 4 values, as it indexes it with 3. Based on the error message color contains only 3 values, which is why the error is raised. 
I don…