Darkening a blue paint takes more than just adding black paint to the original color. Adding the wrong color paint to a light blue can make the color appear muddy or change the base color of the paint entirely. To retain the original hue, it is important to analyze the paint to determine the base colors used to make that shade of blue. Use darker tones of the same colors to darken the paint while still retaining its original hue or intensity.
Inspect the blue color to determine the tint. Does the color have a reddish, purple or green undertone? Many light blues actually contain other colors, which need to be retained when the color is darkened. Identify the base tint of the color so that you can darken the blue without changing the color tint of the paint.
Mix up a small trial batch of paint to determine the colors necessary to achieve the desired shade. Use about one cup of paint if you are altering a wall color, or a quarter-sized amount of paint for acrylics or oil paints. Add one drop of color to the paint at a time.
Add one drop of black paint to the blue paint and mix. Write down what color you added to the paint and the result. Keep adding paint to the base one drop at a time. Try adding other colors of paint, such as green, red and purple to darken the color as well. Keep adding colors until you have the desired color.
Multiply the ratio you used to make the test batch for the larger batch of paint. If you added 20 drops of paint to darken one cup of paint, then you will use the same ratio for darkening the larger portion of paint.
Mix the paint thoroughly with the paint stirrer and seal the container of paint after mixing to prevent the paint from drying out prematurely.