Lately I’ve been feeling run down…I’m catching something. 
I’ve noticed my nasal discharge is an indicator of how ill I am:
clear, watery discharge; white, thick discharge; yellow, smelly discharge.
What are the components in the creation of my ilness’s “mood snot”?
I haven’t noticed any difference in the color of my boogers when I’m feeling a bit under the weather, but there sure is a big difference in the taste.
The colour of phlegm can be affected by residues of infection (dead bacteria and white blood cells mostly), but I think I recall QtM saying that it isn’t a terribly reliable indicator of anything.
Band name!
It is unlikely that you will have clear mucus without having all systems go in the nooks and crannies of your nasal passages.
The reason for unclear mucus is, as Mangetout says, unclear. Actually, that’s not accurate. Unclear can, and very often does mean you are dealing with more than allergic snuffling, but it’s not 100% certain.
By the way, Enola Straight, if you like spicy food, it’s a great way to clear out your head. Hot drinks, hot showers, mentholated lozenges - it’s all good.