As silly as is may seem, the colour and smell are really all that’s important as MOST 2t oils preform fairly similarly.I choose the oil that looks best when mixed.
I like the cool blue color.
Sometimes I pour it out on the ground just to see the pretty colors as the sun shines through it - I wait for a good sunny day, near noon.
Occasionally I put it in the saw.
Colour so it contrasts with whatever Jerry can colour you’re using for quick identification and smell to avoid headaches.