When starting a row with a new colour, it is easier to use a slip knot to attach the new colour to the old colour:
To make the slip knot take white yarn under the blue yarn from point A as shown above, bring white yarn around and over both the blue yarn and the white yarn, then under the white yarn again.
Pull the knot tight and slide up the blue yarn until it touches the knitting:
The next row is then knitted using the new colour (white) and will look like this when completed:
