Types of heat maps and application

Web heat maps are used as tools for web analytics. They show the most visited areas of a web page.

Biological heat maps are commonly used in molecular biology and medicine to present data on the expression of multiple genes in different samples, such as from different patients or under different conditions from the same patient. Typically, a biological heat map is organized as a table, in which the color of the square shows the level of expression, and the columns and rows are the various genes or samples, the hierarchical organization of which can be depicted as a tree in the margins of the table. Also, heat maps are used to visualize data on the three-dimensional organization of chromatin, obtained by methods of fixing chromosome conformation.
A tile plot is a tiled heatmap for representing data that has two or more variables.
for example: https://creabl.com/service/heatmaps
Use of colors
There are many different color schemes with their own advantages and disadvantages that are used in heatmaps. Heat maps with a large number of colors (rainbows) are often used, since people are able to distinguish between a greater number of different shades of color than they can distinguish between grays of different intensities. This allows you to parse and notice more details in the image. However, it is not recommended to use a wide variety of colors for the following reasons:

Widely used color schemes (such as jet, which is the default in many data visualization programs) are too bright to display correctly in black and white or print. Also, in such color schemes, yellow and blue areas are more visible, which distracts the observer from the main thing.
A small difference between colors makes us see gradients that aren't really there, making real gradients less noticeable. In this way, iridescent color schemes hide details rather than making them more obvious.
Regardless of the choice of color scheme, you should attach a color legend explaining the meaning of the colors, or describe them in the accompanying text.

Various color schemes are used, consistent and divergent.