Keto is the only thing that fixes my depression-like state. I discovered it doing short-term fasts and then learned about Keto.
I tested it multiple times. Once I get off Keto I feel much worse within 2 weeks and after around 1 month I am at the total bottom again. Then go back to Keto, 2-3 days of suffering Keto Flu and I'm happy to live again.
Your body is switching to ketosis. You can read about it a lot and it's literally called keto-flu by the keto diet community :) If you want to ease the transition, you should first get into ketosis, but not fasting yet(so still eating but not carbs), and after ket-flu is gone then try fasting.
From my experience all that comes from shock to the body. You are simply not used to it. It gets better over repeated attempts.
Also for the headache - do you still drink caffeine? Brutal headaches usually come from caffeine withdrawal(if you normally drink it but stop during fasting). If that is the case you need first to drop caffeine slowly lowering your daily dosage so the headaches won't happen.
Seeing color(qualia) does not provide any additional information. They are just a tool your brain uses to speed up processing. Treat is as quick tagging system. It's done inside your head, we don't even know if all people tag colors in the same was(is your red, my red?).
Qualia are derived information. Your senses get information, and you get some processed result. There is nothing added(beyond what your mind may add, but that's not part of the original information). You could swap red for green, green for blue and nothing changes.
Imagine a wall of text, a very big one. To read it you have to carefully go line by line, focused on the content. It takes a lot of time to do.
But now imagine you evolved to read such text walls. Now it's not hard, because nature developed special structures to process them, and now you have dedicated, and optimized region in the brain to handle them. You just glance at that massive text and "see" all the content, it sings to you, you understand it instantly, maybe even feel parts of it.
And seeing is the same. The mass of color information hitting our eye, that for someone without innate ability to process it would look like a bunch of hard to plow through data, for us is just instant. We process multiple frames per second, detect objects, project movements. All of it without even thinking about it. Incredible.
All thanks to specialised machinery in our brains. The specialized part does the heavy lifting so we can see our qualia. But it's just a tool, it does not provide additional objective information, as it's only your subjective view of the information that other parts of the brain push to you. It's processed information, enriched, but because of that, it's subjective now.