According to Chinese food blogger @hkfoodiexblogger, each color is a different type of cheese:
"The toast costs (about $6) and the colored cheeses are lavender (blue), basil (green), tomato (red) and the yellow one is actually the combination of four kinds of cheeses (mozzarella, cheddar, emmental and gruyere). The toast was crispy, but I reckon both the flavor of the lavender and tomato were subtle. The basil flavor was the most outstanding one comparatively, but the cheese flavor was still not as strong as my expectation. It was also a bit oily in general. I would say the quality was rather average but we all cannot deny that it is photogenic."