What type of ink do you use? Eco solvent? You may be careful about mixing inks. Check with the manufacturer and ask them if they support other brands of ink. If not you may want to flush the system first. If sell for Bordeaux inks and may be able to help with selecting a new ink. I would suggest that you don't mix inks unless you research this.
There’s a LOT of stuff to try first before you blame the ink. If you’ve started that process, please enlighten us as to why you’re blaming the ink..
Has it ever printed the right colours? “China printer” doesn’t fill me with hope. What ink are you using just now?
Without any knowledge of the printer or inks, it could very well be the inks.. but could also be a multitude of other factors, including software and hardware.
However, the Chinese printers save you some money upfront, but always seem to be expensive headaches from then on unless you’re very techy/hands on.
It could very well be that the output you are getting, is the best that printer can do? Is it consistent?
How do the test prints/nozzle checks look?