Why did Arrow play homage to Blue sky?

This is an example of Genre Fractal.

TV shows, even though they may be completely unrelated, are able to communicate meaning by referencing each other and using those references as narrative shorthand.

If a drug is shown and it is needed to be conveyed that this is, for example, an incredibly pure iteration of that drug; they can dye the drug blue and hence reference another TV show, borrowing the lore built within that property as a way of bypassing heavy exposition.

The reference won't land for everyone, but for those who 'get it', its a nice way of condensing the significance of something and participating in a referential exchange of 'easter eggs'.

It's all the rage these days.