Biased tape: A narrow strip of cloth cut diagonally, used for trimming or decoration.

That is, diagonal stripes used for edge locking and decoration.

The proper noun is twill: twill: a line color different from the main color. Contrast needle: sew with a thread color different from the background color.

So your whole sentence is:

"Use this color as the contrast needle for the diagonal planting belt seam" (the color of the thread is the same as that of the diagonal planting belt, only compared with the overall background color of the clothes)