From what I remember Tamiya is more expensive. If you’re going after actual accurate colors, Vallejo Model colors is a good substitute. Not sure if others would agree with painting lighter than actual colors for 1/3000 ships. I’ve done accurate colors for WWII USN pattern and they look too dark, needing more highlight than usual.
RN ships are light gray Harriers are dark gray.
You can get Valejo color charts here and compare to photo references.