Attribute qty discounts are attribute prices based on qty ordered.

Enter them as:

Red:
3:10.00,6:9.00,9:8.00,12:7.00,15:6.00

Yellow
3:10.50,6:9.50,9:8.50,12:7.50,15:6.50

Green:
3:11.00,6:10.00,9:9.00,12:8.00,15:7.00

A table will also show on the page to display these discounts as well as an indicator that qty discounts are available.