I think it depends the look you're going for. The fluildines make nice, light, wearable e/s bases but they do all *definitely* affect the colour of whatever you've put on top. I enjoy playing about with them for particularly this reason - I particularly enjoy layering shimmery powder shadows on top of dark fluidlines, it varies from shadow to shadow, but can give an intense and interesting "jewelled" look as the dark base intensifies the top colour and peeps through a bit, too.
Frostlite is the most "neutral" and "basey" of the fluidlines, but it's still got colour - pearly gold - and will still *definitely* affect the final look of your shadow. For example, I like to wear Seedy Pearl - shimmery pink - packed over Frostlite to give a duochrome pink/gold pearl effect.... so in short, I think frostlite as a base is better if what you're looking for is a *pearly* base. If instead what you're looking for one neutral all purpose base in the way that you might've used beige-ing s/stick before, then look at Urban Decay primer potion, or another neutral primer, instead.
Some of my fave fluidline + shadow looks, and what the f/l does to the look of the shadow:-
frostlite + seedy pearl: pearly shimmer pink and gold together
frostlite + violet pig: the shimmery white of the f/l peeks through and makes the pigment look a bit more of a "lilac" shimmer than a purple - has a lightening effect
bitz 'n glitz + moth brown: a dark and very shimmery smokey eye, the darker colour peeks through a little
macroviolet + beauty marked or nocturnelle: really intensifies the colour - a dark plum smokey eye
blacktrack + carbon: semi-matte very intensely black eye
blacktrack + violet pig: really dark, intense purple shimmer as the black shows through
blacktrack + Urban Decay Vert (light intensely shimmery green): really dark green metallic eye
... etc
Hope this helps x