Issues about Cityscapes trans_label

[myknowntime]

I still can't figure out the code in cityscapes.py. Does it redefine the color and label of citylabels? If so, can you explain the concrete process? Actually, I used this code in my own dataset, I have some questions about trans labels. I want to segment three classes including 0: background, 1:building and 2:road and their pixels are (255,255,255), (255,0,0) and (0,0,255), so how can I change the code?