The display colors seem faded

Hello, yesterday I went to the sea and I brought my iPhone 5s expecting to hear some music. I held terminal wrapped in a T-shirt to avoid direct exposure to sunlight, but the phone has become very hot. After returning home, I upgraded to the new iOS and the next day I noticed that the colors of my iPhone seem somehow less lively.

I do not know if this is due to sun exposure or update but also other people who have seen the screen of my phone said that the colors appear duller. This also happens by increasing the brightness.

Can anyone give me an explanation, including technical, about?