There are so many people who have tried their hands at this theme before me, I know. I still feel this is a great theme, so I'm trying to do it my way.
While I have read what is "usually associated" with all the sins - in this case the colour green and the dog - I chose not to follow this traditional approach, but instead try and find out what comprises the sins for me. I do not want to give you my whole thought process (this is a bit too personal, I'd say), just a little bit of insight maybe:
Envy is wanting what others have - not only wealth, but also power, status, happyness, experiences, living arrangements, looks,...
The envious person will always seek what others have and always be of the opinion that that is what is rightfully theirs anyway
They are so busy looking at what others have that they can never enjoy anything on their own
Everything around them looks "peachy" to them, if only they could take part.