Cat/snake hybrid more like a domestic cat instead of a big cat - Any paticular type of cat? Fluffy? Short hair? Reference pictures of the cat you want an artist to head towards?
Dark gray scales with electric purple veins running through them - Where? Do they cover the body or are they in patches? Where are the veins?
A small dull red patch of scales behind each year - Guessing you mean ear, what does the patch look like? A blotch, is it a particular shape?
Snake fangs, lips can cover - Do the fangs come out from the canines, or are they from the front like a snakes?
Snake tail - Any particular snake?
Deep green eyes - Do the eyes have a pupil, are they like a snakes eye, like a cats eye, big or small cat, are they normal human like?
The rest is up to you as far as clothes etc
It's good to be descriptive other wise yea I for one can go in all different directions.