Black
There are only two basic horse colors - black and chestnut. All other colors are derived from these two colors.
Black and white.
Brown,white and black
No, Agouti is responsible for making a black horse into a bay, it affects the spread of black pigment. The gene responsible for making a chestnut into a palomino is the Cream gene, one copy of cream on a red / chestnut horse will create a palomino, two copies will create a cremello.
Horses come in many different breeds and a huge variety of colors and patterns. There are three or four different variations of chestnut, bay, grey, roan, palomino, ect. There are dun, grulla and buckskin. These are just a few of the many different colors that horses come in. The genetics to produce some of these coat colors is complicated even for experts. But it is always fun and fascinating to study horse colors.
There are not two basic color genes for horses, but there are two basic pigments: red (phaeomelanin) and black (eumelanin). A horse who displays red pigment will be chestnut, and a horse who displays black pigment will be black. All horses carry both red and black pigment. Bay horses have a gene called the Agouti modifier. It pushes black pigment away from the body of the horse, leaving the mane, tail, and legs black. The three basic horse colors are black, bay, and chestnut. All other horse colors are modifications of these colors.
white grey gold brown black
The three basic colors are Black, Bay, and Chestnut. Black and Chestnut are the basic colors that all horses are born with, however the Agouti gene effects the spread of black pigment (limiting it or not) Which can create a bay horse. After that other modifier genes can act on those three basic colors to create a very wide variety of colors.
Henry IV's horse was famously known as a "black and white" horse, which suggests it had a coat of both colors. However, the phrase is often used as a riddle or joke, implying that the horse was simply a horse that was both black and white. In essence, the horse's color was literally black and white, as stated in the question.
Grant's white horse is likely the color white. This horse may have other colors like brown or black in spots though.
Silver dilutes black pigment. Silver has no effect on Red. And a black horse carrying the silver gene will be brownish/chocolate with flaxen mane and tail.
Horses have 2 base coat colors The RED Gene aka Chestnut and the BLACK Gene which is Black there are variations of the colors due to the nature of the pigmentation(coloring) of the hairs. But within these colors many colors can happen like bays, greys, paints, roans, appaloosa's, sabino, dun, perlino, dunalino, cremello, palomino, and many many more all depending on the genetic make-up of the horse and the genetic make-up of the parents.