In the future, please remember to hit the green “mark as answer” button to indicate your question has been resolved. Since this question has been answered for a couple of days with no follow-up questions, I have gone ahead and marked an answer on your behalf.
Yesterday says... Accepted answer #1
Please link the cards when you post a question in future, it makes it somewhat easier to deal with.
Hex Parasite & Arixmethes, Slumbering Isle
No, I'm afraid not. In EDH, all the cards in your deck must conform to the 'colour identity' of your Commander. Hex Parasite as a card doesn't have a colour, and as a permanent doesn't have a colour. But this is different from the colour identity of the card.
The colour identity is derived from the colour of the card + the colour of any mana symbols in its mana cost and rules text, except for reminder text.
July 20, 2019 6:17 p.m.