This answer concerns only the colours pink and purple
Pink ends on a hard consonant thus "to pinken" would seem logical and the Merriam-Webster indeed lists this as a legitimate form but ONLY as an intransitive verb. According to the Merriam-Webster, the form "to pink" means many things but NOT "to make something pink" . Oxford Dictionaries, however, does list "to pink" as relating to colour but ONLY as an intransitive verb.
Strangely enough, none of the dictionaries seem to list a transitive form, which suggests that we should use "to make pink" for this purpose. However, personally (and I think many others with me) would be perfectly comfortable to use "to pinken" as a transitive verb - even though the dictionaries don't agree with me.
Both "to purple" and "to empurple" are valid forms.