The big principle of the app is to colorise the tone with a different color to help you memorising them and facilitate your training.
Black color stands for Mid tone (Robot voice)
Blue color is for the low tone (Almost the same as mid, but lower)
Yellow color is the falling tone (From mid to up then go down again).
Red color is for High tone (Start mid and go up)
Green color is for Rising tone (From mid to low to mid)
Associate the color with the tone and practice… at one point you won’t think about the color anymore but will know that “THAT” pattern of consonant/vowel is going to make a specific tone.