Unfortunately, usability often depends on minor interface details, which is why systematic usability engineering work is necessary to ferrer out those details. For example, Simonelli reports on the development of instructions for a frozen-dinner microwave indicator that would gradually change from being white to being blue. User testing showed that the phrase "turns blue" was much poorer than "white disappears" for describing this change, even though the two phrases are logically equivalent relative to this process. The blue color was not uniform - it was dark blue in some places and light blue in others - so users were uncertain "how blue is blue?" when the first wording was used.