Coloring of bar charts follows the general rule of using color in data visualization – use color only if it communicates additional information. For any basic bar chart, one color should be enough. Don’t use a new color for every bar chart just to make it beautiful. It will just make a bar chart harder to read.
To draw attention to the most important categories of the bar chart, a good solution is to highlight these bars and color all the other bars the same way in a neutral color. Our brain is programmed to notice deviations instantly. This can be done, for example, by applying changes in size, movement, or color. This way, highlighting a specific bar will help catch the reader’s eye immediately.