The options for customizing WhatsApp Plus are either in your settings and configuration section or in the contact's own settings in the same chat.
WhatsApp Plus General Customization
To customize your messaging client, go to the main Chat tab, click on the icon with the three horizontal stripes in the upper right corner and go to Plus Settings.

Inside the window settings, pay attention to this section indicated in the image.

Themes
Themes are pre-designed XML templates that completely modify the app from the wallpapers to the menu colors. They are the quickest and easiest way to completely change the look if you do not want to configure the app in detail (even if you apply them, you can later modify specific aspects). Click on this entry to see all your options.

- Download Themes: access to the available themes online library. If you click on this option, you will access a library with thousands of different themes. All you have to do is browse through the list until you find a theme you like and click on Install on the right. A few seconds later, the entire WhatsApp Plus interface will be changed.

- Load Themes: if you save a theme to the SD card, you can import it with this option.
- Save Themes: lets you save the changes you have made to the currently applied theme.
- Restore Theme: this option lets you completely restore the settings of the installed theme and make it look like the original one again.
- Reset preferences: to return to the default appearance.
- Delete all saved/installed themes: deletes all saved and installed themes.
Universal
In this section, you will find several different settings related to customization.

- Colors: lets you change the colors of different parts of the interface. You can change the color "universally" for the whole UI, also the colors of the ActionBar, the wallpaper, the status bar, the navigation bar and even the lines that separate the chats in the conversation tab.

- Styles (Look and feel): you can change the launcher and notification icons, choose between several fonts, different emojis packs or even use the old emojis.

- Hide Media from the gallery: one of the features of this MOD is to make your gallery photos, videos or GIFs invisible when you chat. In this section, you can define exactly what type of content is visible when you open the gallery. From here, you can reset the settings for this feature at any time or reboot the phone if the settings you are applying do not take effect.

- Backup and restore: in this section, you will find the options to create backups and restore them. Please, note that these are different options to those available at WhatsApp's regular customers, located in another section.

- Settings: in this section, there is a complete set of different settings. You can configure the language, set a card system for each chat, disable notifications and the card counter, change the GIF provider, delete logs, resize the images that can be sent or disable the limit of images that can be shared simultaneously.

Home Screen
In this section, it is possible to modify the Homescreen's appearance, which is the chat window visible every time you access the app and where all our conversations are listed.

- Header: this section changes the header appearance of the homescreen window. You can make your username show up, make the status disappear under the name, show the statuses of our contacts in a similar way as in Instagram, show or not the icon to activate the airplane mode, disable the app name to grant access to hidden chats or change the color of the different components of this header.

- Rows: the Chats tab, as we have seen, all the conversations are listed. This list can also be customized in many ways. It is possible to change the overall style to look like other popular MODs. You can also change the size of each row/contact as well as the different colors on the screen. You can also hide the online status of your contacts as well as the time they last connected.

- Floating Action Button: there is a floating button with a + symbol on the conversations tab. From this section you can configure its appearance and behavior, you can hide it, change its color and make various additional adjustments.

- Status: in the Status section, you will find the options referred to the MOD status function. In essence, it lets you modify the colors and offers a couple of other options to mute the states, hide the states already seen or the recent updates section.

Additionally, you will find some more adjustments to round the corners of the pictures, hide the lines that delimit the rows of chats, deactivate the online statuses for everyone or assign tones when a contact becomes online and available.
Chat Screen
Within Chat Screen you may find all the customization settings related to the chat windows where we have our conversations. As in the previous case, there are specific settings for certain parts of the interface as well as several generalized settings.

- Action Bar: This is the top part of the chat window where the name of the contact, their status, as well as the icons to initiate calls or video calls, are displayed. Here, you can change the colors, make the image, name or status of the contact visible or hidden, hide the phone-shaped icon, change the background of this section or the colors.

- Bubble And Ticks: this is the place to customize everything about the text bubbles you see in a conversation and the ticks that accompany each message. There are several eligible styles for both, also an option to resize them and a whole range of possibilities to modify the colors.

- Pics: as you might guess from the name, this is where you can make adjustments to images and pictures within conversations. You can choose whether you want your photo to appear in all the messages you send or your contact's photo in the messages you receive. The same options are also available for groups, and you can change their size.

- Conversation Entry Style: these options refer to the text box where you write the messages you are going to send, the bottom of the chat windows. There are several available styles and from those styles a whole range of options to alter the background colors, the buttons (either emojis, send or microphone in audio messages), or the letters of the text you write.

- More options: additional customization options for the emojis section, the links that are shared in a chat, forwarding icon and appearance of that information in the conversation... A little bit of everything that has no place in previous sections.

After all, you have a whole battery of new settings categorized into MODS, Voice Notes/Audio Mods and Forward Settings.

- MODS: you can activate the possibility of setting different wallpapers for each conversation, make the image of the contact your own background and hide the date and name when you copy more than two messages.
- Voice Notes / Audio mods: you can enable or disable the proximity sensor.
- Forward Settings: settings related to the messages you forward.
Widget
The last of the possibilities involves adjusting the appearance of the WhatsApp Plus widget. Basically, it lets you change the background colors of the widget, the contact name, and its status. Just click on each option to see the full palette of available colors, which as usual you can set using HSV, RGB or HEX code.

The best thing you can do is explore all the customization options available and try out the various settings until you find the look you want for your device.