Use color for Chinese tones

[met]

Many learning tool use different colors for Chinese tones. But there is no standard for those color.

Based on text https://www.hackingchinese.com/does-using-colour-to-represent-mandarin-tones-make-them-easier-to-learn/ this is really a mess

According to author of that text, if anyone use color in application it is neccessary to make user preference to set there color (or to switch off colors at all), otherwise this can be an obstacle for students accustomed to a different sets of colors.