We tried to die some sheeps wool with natural homemade dyes, I think we used onion peels and turmeric (yellow) hibiscus leaves (red) and red cabbage (blue) and we used vinegar as a fixative. Let’s just say it was a case of the process was definately more enjoyable than the end product, lol! The dye baths were so vibrant, but when the wool had been rinsed none of the colour had really been absorbed and it turned out a horrible grey with what looked like blood smears!
The vinegar probably wasn’t strong enough to fix these colours, or maybe not enough material was used to make the dye (onion skins, etc) - you do need to use a lit to get a rich colour. Or maybe it was time as arwen-tiw says above. I’ve dyed with onion skins and turmeric and got really rich colours but used a better mordant than vinegar.
As far as I’m aware the red cabbage although it gives you blue water won’t give you a blue colour on your wool, and you’d need to mordant the wool with something more than vinegar to fix the colour.
I think the mordant is the key here - mordant the wool beforehand next time (if you do it again) and the colours will fix and be richer.