A little late, but...
Short answer; most printers with any experience would not use a 110 on a light shirt.
When I started out with plastisol, 25 years ago, my screen inventory was pretty much 160 for dark inks on light shirts, and 110 for opaque inks on dark shirts.
Since then, standard cotton and 50/50 whites and other opaque inks have gotten creamier, and it seems they print pretty nicely through 160, and I use mostly 180 and 200 for dark inks on whites and lights.
I still sometimes use 110 for light inks on dark fleece, but may even up that to a 125 or something similar in the future.
btw, spot colors are merely color inks that are used as those colors (ie bright red or kelly green, or Pantone 123) as opposed to some sort of process separations and printing which mixes different color dots to achieve the desired end color. Even a halftoned print can be a spot color.