Hard to spot GCs in Flamegraph due to noisy color palette

Filed from https://bugzilla.mozilla.org/show_bug.cgi?id=1650660.


User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:79.0) Gecko/20100101 Firefox/79.0

### Steps to reproduce:
* Record a performance profile from any site

### Actual results:
It's very hard to differentiate if a bar represents JavaScript, firefox internals, GCs or paintings. See the attached screenshot where the GC bar has nearly identical colors to the bars coming from JS code

### Expected results:
Use easy to distinguish colors to quickly recognize the different bar groups.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-292)