I am using WEST system epoxy on my kit, and the WEST manual and others recommend the yellow covers that are 1/8" thick. The WEST manual states that these yellow covers, 1) allow for greater control over film thickness, 2) are less likely to cause epoxy exotherm, and 3) leave less stipple. I also found the System Three covers are yellow and 1/8" thick. Is yellow the industry standard for 1/8" thick covers? In the past I have used only yellow covers with success, although they are more expensive. The dark purple covers I received with my supplies are 3/16" thick. Does the extra thickness matter for epoxy? For paint or varnish? Anyone have experience?
In terms of thinner rollers, I've used Wooster 1/8" yellos foam rollers exclusively, so I can't comment from experience in whether the 3/16" rollers would work. I suspect they would work but that you would be slightly more susceptible to your whole batch getting gummy before you've finished. If I were you, I'd probably just buy some thinner ones - it'll be a drop in the bucket in terms of consumables cost. If you're the type of person who is bothered a lot by wasting a few dollars here and there, give the thicker ones a shot.
I can confirm from experience that thick foam rollers (hot dog rollers that absorb tons of epoxy) are a bad idea because of exotherm. Obviously they waste a lot of absurdly expensive epoxy, but they can also get extremely hot, smoke, make your batch sticky, possibly mess up any epoxy on the boat you touch with them once hot, and permanently attach your roller to your disposable hotdog roller (don't ask me how I know).