As stated before, the original iPhone came in one color. iPhone 3G though the iPhone 5 only came in two colors (black [or slate] and white [or silver]). It was only in 2013 that Apple started really expanding the color choices for the iPhone. The iPhone X launched with only two colors almost certainly because of the limited ability to produce any models at all. Now the supply chain seems to be clearing up, but I suspect that the iPhone X will most likely not get a new color.
Perhaps in the March keynote for the AirPower/Wireless Charging AirPods, HomePod, (possible) new iPhone SE, and (possible) iPad Pro and Mac updates, we could see a Product Red and/or Gold iPhone X, but probably not. I would not be surprised of they released a Product Red iPhone 8/8 Plus though, to spice up sales.
Come September 2018, we will see the new iPhone and iPhone Plus, and that is when we will like see an expanded color selection. I don't expect a return to the color palette of iPhone 6s/7 for a few years, perhaps 2020-ish.