This is my first Tau Fire Warrior.
I've chosen white as the army colour because it is really visible on the tabletop, but it uses a "realistic" colour scheme (it's an army from a ice world).
Dilute your paint a lot more. It is better to have to put two or three layer of thin paint than one layer of undiluted paint wich will hide details and ruin the model. Nice job on the optique. If he's from an ice world you could try to make a coresponfing base so that people would understand
You could put Some kind of snow or just Ice blocks. Also try shading your white and higlighting your black.
The optic isn't difficult at all: just make it blood red, then mix blood red and yellow and paint the lower-right part whit it. Then make a white spot on the upper left part. And finally varnish it two or three times.