By default, eM Client will show all messages with HTML formatting. This means you will be able to view the font type, color, inline images, links, and other formatting details as the sender designed them.

If you prefer to view all messages in Plain text, ie. all colors, formatting removed, for easier reading you can do so in Menu > Settings > Mail > Read by checking the option to "Read all messages in Plain text".

Starting with eM Client 8.2, you can also switch the view of a single message on demand and view it in a different format than your default setting.

Simply right-click the message and switch the Format to HTML or Plain text, depending on which one you need to take a look at. You can also find the same setting in Menu > Message > Format.