Top Down Cardigan

The other day I started my first top down sweater.
First of all I studied the "theory of top down technique"... I bought on amazon a good book that is "Knitting sweaters from the top" by Cathy Carron and the explanation was quite clear.

Point is that I like most of all the boatneck and that is the only one not explained in the book.
So I decided to follow both the basic cardigan scheme of Cathy Carron and the Pattern "Gilet Nuage" by Maud Jacquey that is on Ravelry.
 
 ( Could not use just the last one, as it's for a small size, while I need it in medium/large size).

I made my math and while casting on I added some stitches to the front and the back, while just two stitches more to each arm.

The wool I'm using is Class from Lana Gatto

It's a present of my mum and I like it so much.... the white is so pure!
She told me that she was looking for pure angora, but that she could not find it, because it's too expensive and there is too little market for it so there is no more production of pure angora.... that is what the seller told her to explain why he had not pure angora.

Anyway I'm in a doubt... if it's better to do a whole withe cardigan or use a paste colour to make little contrasts, maybe just in the edges...