i just got a idea where for the glowing squids they could spawn in the deep dark parts of the ocean and will have mobs such as fished go near them as in the dark ocean not a whole lot of food is down there. And Or what you could do is add a feature where glow squids will have a chance to drop some of the glow so if there is a dye and a light block (such as torch redstone lamps etc) it would make a diffrent color of that  such as red gray blue etc so it adds more building potentail but can be like the banners where you have to make the color. idk bout you but having red light in a hallways leading to a nether portal would be cool.