I think you are exagerating. Nobody got offended that the females of this universe are blue.
OK, let's step back and re-evaluate this situation: yes, the Bionicle lore has no excuse if it is sexist or racist or whatever. The thing is that it isn't. The rule that all the females are water-related was broke many many years ago. You could call the series sexist if all of the females in the story would be poorly made, or put into the sidelines, but when we have characters like both Galis, Nokama, Hahli, etc, that are fanloved and appreciated, can you really keep saying that it is sexist? Hell! I would personally say that some of the females got more love by most of the males. We have bad@ss women who can defeat monsters and demons, yet the fact that they are all blue is somehow sexist.
"Oh hey! It's the blue Toa! The other two were women, so I think this one is too."
OK, now you really are exagerating. Personally my mentality have been changed by my long running passion for Bionicle. This might be the reason I associate the female gender with the colour blue, rather than pink or green or yellow. The thing is that out of all of the original elements the writers (and if I think a little me too) thought that water would be the most fitting for a woman. It's nothing stereotypical, it was just Lego's preferance.
Again, I think you are exagerating. This genderlocking is an inconvenience, a limitation in storytelling, but not sexist. It's not a subtle way to limit women. It was just a marketing choice made by Lego. A choice later backed up by the lore. I think you should take a brake. I assure you: nobody wants to limit women and their talents, and the ones who actually do should be pointed on the street. But digging deep into small details like this, while there are sexist and feminist movements threatning the peace between women and men, it just seems to be weird, exagerating nitpicking.