A darker navy blue
It is not possible to make the color brown turn black. Brown is a combination of red, green, and blue hues, while black is the absence of color. Mixing more black paint into brown paint will only darken the shade of brown, not turn it black.
mix brown and blue paint
Use black paint on its own, otherwise you will need to keep adding black until the grey becomes black enough. Adding a very dark blue to grey will make a black, but it won't be a proper black, more like a bluey black.
Black can be created by blending together equal amounts of the primary colors red, blue, and yellow. Alternatively, you can use black paint or pigment to achieve the color directly.
If you are trying to make black paint with blue paint just add an earthy colour (brown) :)
Black is a primary color so you cannot really make it with any other colors.
If you add red to green, you get brown.
Dark brown
Any colour you want! Why not paint it brown so it blend in with your garden, or paint in red with black spots to make it more ladybug-like.
To make the color black with paint, you can mix equal parts of primary colors blue, red, and yellow. This combination will create a dark shade that appears black.
black and blue and silver
Brown and white, with possibly a bit of yellow will make toffee.