When you knit with multicoloured yarn, sometimes the colours come out randomly mixed and sometimes the interplay of stitch counts and yarn dye lengths and tension means that the colours start to form blobs ("pools") or lines ("flashes") in your work. Of course, the laws of the universe usually mean that what you end up with is two circular pools in unfortunate positions on the front of your sweater!
Some yarns are deliberately dyed to form stripes or spirals, usually meant for knitting with socks. And some people take the time to work out how many stitches they will need in a row to get the colours to stack up on top of one another, intentionally pooling the colours.
In my case, I'm getting what can be described as an argyll pattern, forming crosses of one colour against a background of the other. And it's completely accidental, and it's not really what I'm after. So how can I correct it? I need to break up how the rows are stacking on top of one another without damaging the stitch pattern. The easiest way is to change my knitting tension. Using a smaller or larger needle (or knitting more tightly or more loosely) means I use a different amount of yarn for each row which disrupts how the colours fall along the row.
Time to try again with a looser tension, I think!