Two useful and common blues are ultramarine and phthalocyanine. Ultramarine is on the violet and warm side, whereas phthalocyanine is slightly green and on the cooler side. Another blue is cobalt, which is a pure blue and has neither violet nor green. When mixing for a dark blue, do not add black; add more blue to maintain the richness of the colour. Mix your colours using a paintbrush on a paint palette, waxed paper or paper plate that has a non-stick coating. Mix only as much as you need, or have a container or jar available to store your mixed paint, since acrylic paint dries faster than oil paint.
Place blue paint on your palette.
Add a colour to lighten or darken the blue, such as titanium white or Payne's grey, a little bit at a time. Mix thoroughly with either a palette knife or a paintbrush.
Adjust the colour until you achieve the colour blue desired.
Mix a dark blue -- almost black -- by using one part Payne's grey, two parts ultramarine blue and four parts phthalocyanine. Do not use black, as this will turn your blue to mud.
Mix a dark blue with a violet undertone by using one part permanent rose to five parts ultramarine blue.
Mix one part phthalocyanine blue to one part titanium white for a dark blue without violet undertones.
Mix one part ultramarine blue and one part titanium white for a slightly lighter dark blue than the phthalocyanine blue and titanium white.
Use one part ultramarine blue to six parts of titanium white to achieve a vivid medium blue.
Use one part phthalocyanine blue to four parts of titanium white to create a medium blue.
Use two parts of ultramarine blue, five parts of turquoise green and eight parts of titanium white to mix a shaded medium blue.
Use one part ultramarine blue to eight parts of titanium white to achieve a vivid light blue.
Use one part phthalocyanine blue to eight parts of titanium white to create a light blue.
Use one part of ultramarine blue to sixteen parts of titanium white to mix an almost-white light blue.