According to Virgin Mobile employees, Apple will release a (PRODUCT)RED iPhone 8 and 8 Plus as early as today.
Virgin Mobile distributed an internal memo to their employees, saying that Apple will release the special edition red iPhones on Monday. The memo notes that there will be pre-orders, so it's unclear if the new color would be available immediately or begin shipping later in April, but it does appear that Apple will introduce the models this week.
Mark Gurman from Bloomberg confirms that Apple will probably release a (PRODUCT)RED iPhone 8 and 8 Plus this week.
There was no information about a possible iPhone X in red.