What is a surface temperature of a star that changes from Blue to red?

A star that changes from blue to red is undergoing a decrease in surface temperature. Blue stars typically have surface temperatures exceeding 10,000 Kelvin, while red stars, like red giants or red dwarfs, have temperatures below 4,000 Kelvin. This transition indicates that the star is cooling down as it evolves, often moving from a more massive, hotter stage to a cooler, more stable phase.