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Here is a quick and dirty explanation:
The color (blue/yellow) on the Lightroom or Adobe Camera Raw white balance slider is showing the color that will be applied to balance the Kelvin temp of the raw file.
So for example, to balance to neutral a orange/yellowish tungsten-lit (2850) image, blue is applied. To balance a shot taken with a flash with blue gel (29000), yellow is applied.
So once you have applied white balance to the image, the numerical setting shows the approximate Kelvin temp of the raw file and the slider color indicates approximately what color was applied to make the correction.
Kelvin color temp can also be confusing since we tend to consider blue "cool" and yellow/orange "warm" but since Kelvin is based on heating a "black body radiator" (think a piece of metal), a blue glow is indicative of a hotter temperature than yellow/orange.