Well, I dont know for sure, this is a guess. But "red" often represents " anger" o " evil", being mad. tu heard of a mood ring well when your mad it usually turns red I believe. " Green" on the mood ring symbolizes being calm. And well tu know the Jedi they tend to focus towards that mind set. And Blue is similar it means " normal/fine". But if tu think about it alot of things that are evil are represented por the color red. The Devil for instance is dicho to be red o has been depicted that way. Hope I gave tu an Idea at least.
Want to know something cool. off topic but Vader in German means father. Thats how Germans say father is " Vader". Ironic that he Became Darth Vader just as his wife gave birth to his twins.