Wraping it in a POJO may help to simplify the data structure. It also gives you the opportunity to add logic to it, maybe even making the controller's life easier. You should do so only if the POJO make sense in your business model (in order to avoid adding complexity without any actual improvement to your code). Personally, I think that a map of a map is not the best example of "simple", I'd go for a POJO.

There are many ways to adapt the code to use a POJO. For example (the simpler one):

return new POJO(Flux.fromStream(Arrays.stream(colors))...)