When working intarsia flat the new yarn is always available when you reach a new colour block. However, when working in the round the new yarn is at the “wrong end” of the new colour block when a round is completed.
It is possible to knit seamless intarsia (“intarsia in the round”) by turning the work in the same way as when knitting flat provided you take care to loop the yarns at the turning point.
How to do it
You can download workshop notes that explain the technique, or view them here as a flipbook.