Cerulean blue

Sk gave us the theme "the favourite colour" for Mono Monday.
I know my favourite colour, a greenish blue, the colour of the ozean at some places and sometimes the colour of the sky and of many of my things.
But how can you show a colour in mono? I didn't get the idea, that mono isn't only black and white...
So I tried to paint a beach, meeting the cerulean blue water. 
Okay, I definitely have no idea, how to use aquarel colours... :-D
(One day I'll learn this) Just use your imagination :-)))
Thanks Sk for hosting Mono Monday in September and for the interesting themes :-))