The design of software is essentially the design of the GUI. The VOCALOID screen uses a black color scheme so that prolonged use does not fatigue the user's eyes, and important information is expressed in lines and text that resemble light with a unified tonal scheme. There are many musical composition programs that provide a realistic GUI such as a piano or drums, but the VOCALOID is extremely simple. To enhance the musicality and individuality of the creator, we limited ourselves to the bare essentials, with neutral functional expressions only. As one of the designers developing the VOCALOID, I was impressed with the speed with which user feedback was incorporated into the product. Developers immediately tested the suggestions of users sent in over the Web, via SNS and whatnot, and those that had merit were immediately implemented in the program. The designers then redesigned the interface when necessary. The speed of that development was refreshingly fast. Responding to user feedback, we released the VOCALOID3 with better display colors and ease of operation. We reviewed the product from a Universal Design perspective and made it easier to look at and easier to use. In the VOCALOID3, we color-coded the tracks to make all 16 of them immediately recognizable.