If you want to see how I made the Klein bottle itself, you can check out my instructable for it at:
A short film I made to demonstrate the seemingly trivial task of filling a Klein bottle. The trick is to pour water to the top of the tube that comes out of the bottom, place a finger over the hole, invert the bottle until the bubbling has stopped, turn the bottle upright again, and repeat from the start until you have a water level you're comfortable with.
Alternatively, you could submerge the entire bottle and forgo the filling part, but you still would need to invert the bottle. I didn't have a tall enough sink to do this.
Another way to fill a Klein bottle would be to get a tube that has a smaller diameter than the tube of the bottle, thread it through and into the main body, and then attach a funnel or syringe or something to the tube to put water in it without needing to have separate air and water exchanges.
In order to add colored water to your Klein bottle, complete the steps listed above, and then place a few drops of food coloring inside the tube at the bottom. Plug this hole with a finger or cork, and then repeatedly turn the bottle end over end until it has all mixed together.
Follow me on Instagram: Zachback64