You have asked big questions.
1: Color accuracy is poor in Archicad. I've worked with several firms attempting to replicate specific colors through specified paint chip to rendered view to printed output. Impossible!
As to whether the infernal engine is any better than LightWorks, it depends on the accuracy of the material surfaces. LightWorks, using RayTracing is a superior renderer and potentially faster.
Using white sun might make surfaces look truer, but the reality is that sun IS warm and shadows, cool. Dialling in yellow sun and ambient and/or skylighting, sky blue produces a truer environment - closer to what the client ultimately experiences.
2: There is a setting in your system somewhere that makes the sun yellow. Archicad is NOT independently making a low sun angle yellow.
The solution depends on how badly you've messed up the settings. For instance, in the LightWorks Environment, you can alter the color temperature of the sunlight INTERACTIVELY with the sun color set through the camera dialog. Always set LightWorks Sun Color Temperature to 0.0 for predictable results.
ALSO: there are several ways to get sun in Archicad. Your project might have a Sun Object placed in it with independent color settings. LightWorks produces the best sun quality with the Sun Shader "Realistic Sun" actually generating soft shadows.
And so it goes.
Dwight Atkinson