This replaces the default colors with colors with precomputed alpha.
They should look the same as long as you don't change the background
color.
The reason for this is I need non-transparent colors for a fork of
treemapd3.py that I am working on. I'm attempting to render some arrows
behind the tiles, and with transparency the result is just too noisy.
---
This then broke the nested rendering, which relied on opacity to make
each layer darker, so I've replaced that with an explicit svg
filter-effect.
The opacity hack was non-linear and kinda ugly past depth >~3, so it
should have eventually been replaced anyways.
Christopher Haster
021e03cdc9