Paints & Mediums
Us artists call paint 'color'. The color is actually the pigment. The finer a pigment is ground, the finer the color.
Particle size is important when it comes to the quality of an artist's paint. A fine pigment will disperse into a binder compactly, whereas a large and irregular pigment will leave chasms and not fit as nice. A fine paint is just pigment and binder. A student grade may use a cheap opacifier to fill the nooks and crannies.
In the old days, a master would mull pigments by hand into a binder in a laborious and sweaty process. Nowadays, most paint is made by machine, and can be just as fine.
What characterizes different types of paints is the type of binder that holds the pigments. A watercolor paint uses gum arabic, which easily dillutes in water and is rewettable. Oil paints mostly use linseed oil as a binder. Acrylics an acrylic polymer, and the list goes on. In all cases, however, the pigment (the color) is the same.
So, choose whatever 'binder' suits you, and the finest particle size you can afford - but most importantly, choose 'colors' that resonate with you as an artist.