Use colors more effectively

[djahandarie]

Right now colors are selected at random within a color palette. This primarily accomplishes the following goals: (1) making the flamegraph look pretty and (2) making boxes visually distinct from each other.

However, colors are a very wide dimension, so a lot of information can be stored in them. This is one of the core principles of visualization.

Some things that interest me are:

1. hue by thread
2. hue by whether it was in the kernel or userspace
3. brightness by self usage%

(Yes some of these things are already encoded in textual or spacial dimensions, but color allows for far faster skimming and overall summarization and searching tasks.)

There is probably other information of interest as well, so I hope this issue attracts some attention to build a list up of more things that would be useful to encode into color.

[djc]

flamegraph is basically glue between running perf or dtrace and generating a flamegraph using the inferno crate. I think this issue would be more appropriate for the inferno crate, as flamegraph doesn't have much influence on how this is done.