Titanium steel, fastness in color. This rings changes color physically due to the temperature sensible material inside it. Black when below 12℃(53.6℉), then coffee,red,yellow. When it reaches above 32℃(89.6℉), the color becomes green, blue, purple. The most efficient way to test the color changing is to put it on an ice cube, the color changing will be very noticeable. The most common color on human fingers are green and blue.
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