gif not drawing transparency properly?

[meetar]

https://tangrams.github.io/differ/?1=https://github.com/tangrams/refill-style/blob/gh-pages/refill-style.yaml&2=https://github.com/tangrams/refill-style/blob/123204d17ccc74f06da556a33fc613dd78b32394/refill-style.yaml&lib1=https://mapzen.com/tangram/0.9/tangram.debug.js&lib2=https://mapzen.com/tangram/0.9/tangram.debug.js&go

[meetar]

Might also be interactions with map transparency, scene: background: color, and page color

[meetar]

eg: this diff:

results in this gif:

Current guess is that certain map styles assume a particular background color, and the default background for the gifs is black. Possible solution: detect scene background color and set the gif's bg to match.