Why does the whatspp of my iphone look different then other whatsapp on iphones?

I noticed that the whatsapp in my iphone is bit different from the other devices.like, my fonts are not as dark as other iphone fonts. They have neat pattern of send and recv txts.dark wallpapers background… Not only about the whatsapp. My fonts are not as deep as the other iphone device. I bought my phone from online site flipkart… Please do suggest me how can i change or darken my fonts

Whettt

Text appearance is a per phone setting.
i don't like Apple's defaults.

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