What is a good application for Gliss? It seems like a braid replacement but from what I read it can be used in place of flouro or co poly applications as well.

Open water applications mostly. Anything with abrasive cover (wood, rocks, anything that can rub against the line) will cause it to fray real bad and snap left and right. 

I've tried Gliss on both spinning and casting setups, and the only noticeable difference in casting distance is on spinning tackle (maybe 20% extra distance v. regular braid). 

I spooled up two of my spinning reels with it at the start of this season - one with 18# and one with 24# Gliss. I finally stripped it all off last week in a fit of rage after it just snapped in a random spot while I was making a cast. I did see a notable improvement in casting distance, but overall it just became a constant source of frustration for me.

The line is very limp - even more so than braid - so wind bow and wind knots are a constant issue. It also has virtually zero abrasion resistance. 

You will not want to use it on any techniques that call for fishing baits slack or semi-slack line. It is just way too limp for this IMO. Works okay on things like cranks, chatterbaits, buzzbaits, and other baits that employ a steady retrieve. 

my other question would be when would you actually use pink and yellow line?

only when you want to see it?

I've never noticed a change in my success when I use bright yellow lines. Plus, it's super easy to see twitches/line movement, so I'm gradually shifting to hi-vis lines. 

I've been using Gliss on my Ned Rig rod since January and have not had an odd breakoff yet. Casting distance is incredible at first, but has reduced a bit with use. I'm using 24lb and it's actually been very strong, allowing me to land a 21.5 pound flathead catfish in about 5 minutes on a Ned rig.

 

I'm using the lo-vis green currently, but I have 2 spools of pink, one for when the current line wears out and one for my wife's rod. I like to be able to see it and I'm using a leader so visibility isn't an issue.