No. But you can preprocess the signal by multiplying it with a logical signal, which would be true when the signal is >0 for example. Then, you feed those separate signals to a Scope block using a Mux block. In the Scope block, you can change the individual signal color in the 'Style...' menu. There you can give the signal which is > 0 a green color. The disadvantage is that the signals will wrap down to 0 when 'not true'.