4 dot 8 preview 1 - On the directional light source actor, the temperature slider appears to be inverted in the sense that lowering the temperature adds red and raising adds blue whereas the temperature slider on the post processing volume appears to do the opposite.
The inverted temperature slider is actually implemented correctly within the Editor. The cooler the temperature, the redder the color, the hotter the temperature it will become more blue.
Here is an example of the Kelvin Color Temperature Scale Chart:
