Colors in the markers and the category chart should match

I just realized I was getting confused by these things:

* when there's a restyle, this is showing as a light blue "Styles" marker, but this shows as purple (Layout category) in the activity graph.
* the blue color of the "Reflow" marker matches the blue color of the "DOM" category, despite being unrelated. Reflow is also part of the "layout" (purple) category.

Example profile captured today in case this helps: https://perfht.ml/2HjN1Z9

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-109)