There is hope...

I paint with a brush, and I find that as I gain more experience, I am getting better at estimating how much paint will be required for the whole job.

It does start to get complicated when you start mixing a lighter hilight tone, and deeper shadow tone based on the same base tone. But I figure I'll get better at that too!

Another aspect I'd like to touch on is how thin a coat you apply each time. If you are slowly building the colour, the overall effect is distributed all over the build, unlike painting one area to final colour at a time.

Finally, techniques I'm sure are understood by model makers that I learned painting on canvas, are those of washes, glazes and filters.

Each of these have the effect of lending an overall unity of hue, even across different colours, especially in the case of filters. So two areas aren't exactly the same? Applying a filter or a wash and you will even out the chromatic playing field, so to speak.

Experiment! With time you may find other ways not mentioned here.

Cheers, and a happy, build filled, new year!