There's also a pink for 1/2"- 2" waterlines and sprinklers, green for oxygen lines and grey for stainless steel pipes.
There’s also blue colored as well. Blue Monster brand.
I have some that's pale pearly gray. Not sure if they just cheaped out on a colorant or something, but it's definitely bargain-basement stuff so that wouldn't surprise me.
edit: Or maybe it's for stainless steel pipes?
Is there any particular reason?
From the packaging, it says it's more dense. The yellow color is used to indicate gas, so I suspect that's why they chose yellow.
Yellow is thicker and required by code to be yellow so it's visually distinguishable from the plumbing version.