See, blue is a cold colour. Objects that are cold tend towards blue. This means that they are not creating much frictional heat, for example, by moving fast. As speed, and therefore frictional generated heat increases, colour goes from blue to red, then YELLOW, demonstrating a much higher velocity. The effect can be seen in footage of space capsules re-entering Earth's atmosphere. A red flame appears around the nose cone as the vehicle's velocity increases, caused by the friction of entering the thicker atmosphere. At super-high speeds, this flame will be seen to turn YELLOW.
I rest my case...