Intarsia colourwork
Separate yarn supplies fill blocks of colour without long floats across the back.
Counted practice swatch
Cast on 20 stitches. Plan 7 A, 6 B, 7 A, with a separate A supply for the second block.
Work the repeat
RS: k7 A, k6 B, k7 A. WS: p7 A, p6 B, p7 A. At every boundary pick the new strand up from under the old strand to interlock them. Repeat for a rectangular block.
Read the fabric
A hole at a boundary means the strands did not interlock. Keep the join flexible and wind small bobbins so that unrelated yarns do not travel across a block.