Rekolors is an utility for convert a color from HEX to RBG and back. For conversion is sufficient tap on HEX field or RGB field and set value.
The HEX value can be saved in clipboard.
There is also a selector (button at the bottom right) to quickly choose a color and observe the respective HEX and RGB values.
Together with the app there is a nice widget that generates a different color every quarter of an hour showing HEX and RGB code.
The names of the colors are obtained by relying on a service on GitHub (and which we thank for the great work):
https://github.com/meodai/color-names