The OnePlus 7 that went on sale today in the UK, Europe, India, and China is already receiving its first update - OxygenOS 9.5.4.
The firmware weighs 223MB in size and bumps up the Android security patch level from March 1, 2019 to April 1, 2019. In addition to that, the update also brings in DC Dimming so that the phone's screen doesn't flicker at low brightness settings.
Additionally you get the Fnatic Mode as well as some optimizations for the fingerprint unlock and the photo quality. And then there are also general bug fixes and an improvement to the "smooth-scrolling experience."
The OTA should reach all the units within a week or two, and if you don't get an update notification even then, you can try pulling it manually by heading over to your phone's Settings > System > System updates menu.
red is only in india and china
The picture isn't misleading. The red one is available in China and India only