Is the verb "can" an acceptable translation for the verb rajti? The modal verb can is frequently used for expressing permission as well as ability. I get that the translation given is meant to help keep these two shades of meaning distinct between rajti and povi. If that's the case, I still think "we can see beautiful colors" should still be an accepted translation for this sentence.
Not in the usual meaning of the English word "can", i.e. "to be able". That would be "povi" in Esperanto, or perhaps "ebli" if the meaning was having the ability to do something. "Rajti" means either "to have permission" or "to have the right" to do something.