[Aponax]

Yes they are random. See the blog about the inventor of the flame graph, how we know them today

> Neelakanth and Roch's visualizations used completely random colors to differentiate frames. I thought it looked nicer to narrow the color palette, and picked just warm colors initially as it explained why the CPUs were "hot" (busy). Since it resembled flames, it quickly became known as flame graphs.

https://www.brendangregg.com/flamegraphs.html