I should say a little about colours. I always have colour theory in my mind when painting. I use colour complementaries a lot, such as blue and orange (my favourite), green and red or purple and yellow.
Of course the colours don't have to be strictly opposite on the colour wheel. I like to use split complementaries such as a warm and cool blue, with a warm and cool Orange, and including the neutral colours made by combining opposite colours.
Of course when you mix opposite colours you do get Grey's so you have to watch for that. I have included some Payne's Grey ink in this piece, a lovely grey with blue undertones.