I have three "samples" that are dark and three that are "light" I'm guessing that color must mean something?
In theory the darker juices have more pigments that can gunk up the atomizer coil over time. Some note that darker juices might be a little 'thicker' and wick slower.
I'm not convinced that the color of the juice means much, but yet, it can be an indicator that the juice might leave behind more residue and flavor than a more clear juice.
For 'juice tasting parties'...I like to do the following:
Set aside 3 or 4 atties.
One for sweet/thick desert like flavors.
One for tobaccos and spicy cinnamon/clove stuff.
One for fruity and citrus type stuff (oh, and sour candy stuff as well).
In doing this, I find that I don't have do much more than blow out the atty real good then start dripping my new flavor. It might take a few drops of vaping for the old flavor to totally go away, but it's usually just fine for me.
I like to keep a low resistance atomizer around as well. Thicker things like coffee and chocolate sometimes vapes much better to me.
For standard stick type 510 batteries, LR would be around 2ohms on resistance. I wouldn't go below 2ohms on the regular batteries. Also, I wouldn't go above 2.8ohms or so.
Standard atomizers are usually close to 2.5ohms.
For reference...the lower the resistance, the hotter the coils will burn.