I have a requirement where I need to create a bar chart inside a bar chart with different colors. How to achieve this?

This can be done by working on the size and color of the marks card. You can create a dual-axis and then play around the colors and sizes.

Let’s say we have one dimension called category and 2 measures- sales and number of sales.

Now just create a dual-axis using the above dimension and measures. Then make the size of the number of sales less comparatively to sales and then change the color. You will be able to achieve like below-