The property of some materials to change their color in response to temperature changes is called thermochromism. A polymer fiber manufactured in such way that a thermochromic pigment is embedded in the polymeric matrix material develops accordingly thermochromic functionality and can be used as a temperature change indicator. The characterization of a polymer thermochromic fiber with respect to its color change in response to temperature change is presented in this paper. A specially developed characterization apparatus was developed for this purpose. The temperature span of the involved experiment was from 23.5°C (room temperature) to 60°C, while the tested fiber was found to be responsive regarding its chromatic variance mainly within the temperature range 30.5oC - 50oC. During the involved digital image processing, the chromatic shift of the sample was characterized according to the HSV (hue-saturation-value) color model. Fiber’s original color was found to change with temperature by presenting a monotonic reduction of saturation and value with temperature increase.