The core of all things magical, venelum is easily the most volatile material on the planet. Though it is primarily located in the sky-- the atmosphere of Forigo is made of roughly 63% venelum, with denser concentrations the higher up it gets-- venelum is also found in smaller amounts in all living things. It is extremely unstable and usually difficult to control, especially in large concentrations. For this reason, travel by air has proved impossible, even for the technologically advanced tetrax, up until very recently.
Venelum in its purest form is naturally wispy and transpararent in appearance, becoming more opaque only in very high concentrations. Even in large amounts, venelum will remain colorless, simply appearing as a translucent haze when there is enough of it. Because of the glossy, vitreous association of high levels of venelum, spellcasters will often tinge their venelum very slightly with another color to appear more powerful. However, this change is purely cosmetic, and does not affect the capability of the spell itself.
The only beings known to possess naturally near-opaque venelum are the gods.