Choosing a Sketchbook. What Colours Your Choice?

When I come to think of it I'm pretty picky about choosing a sketch book. There are lots of things that I don't like and a lot more that I count as essential.

Three Sketchbooks.

First of course I have to decide what the sketchbook is for. Sketching of course !!!!!!?  gathering information and practice, but is it on my lap for a leisurely draw of the cat sleeping or on the go, capturing movement in a busy place when I should be doing something else.
Size.Purpose dictates size so I have 3 sketchbooks on the go, 6 inch square, 8 inch square and ten inch square. Anything bigger for me it's too cumbersome . The small one I can slip in my pocket or handbag with a pencil, the other two take a more determined effort to take out and about.
Format. I like a square sketchbook. It's just a personal preference but somehow it seems more pleasing. You can always leave part of the page empty to get the right shape.
Binding. Ring binding seems to work best, despite it being a more expensive option and being bulky. A ring binding lets you keep the page open and flat  and draw right up to edge from any angle. It's a good idea to keep the binding at the top or left ( or right if you're left handed) while you're working to keep it out of the way of your hand.
Paper. There's so much choice out there. It's a question of what feels nice to draw upon. It doesn't have to be archive quality. I like a fairly sturdy nearly white cartridge paper that my pen moves over smoothly and will stand up to a bit of watercolour but I don't mind if it wrinkles a little.
This is how I choose my sketchbook. How do you choose yours?  Leave a comment and tell me what you think is important.

Mary Kemp. Hyacinths.
Pen and watercolour crayon.