Unfortunately, that is one of the platform differences with iOS, where we don’t have that option. I did upload a stencil you can search for on Stenciltown called “Web Safe Colors” that has 216 RGB values labeled with the hex numbers that were the original Mac defined RGB values, so at least you can drag one in and reuse the style from the style inspector on iOS. Try using stencils to keep your colors consistent across documents.
While we don’t currently support entering HEX values, it has become more possible on iOS in general than it was before Swift existed. That is a good feature request that would benefit many web designs. Please email us at email@example.com with a request for this functionality to make sure it is properly tracked. Anyone else who would like to see this ability on iOS, please contact us via email as well.