The 850 mb moisture transport is the product of the wind speed (m s^-1) and the mixing ratio (g g^-1) at 850 mb. Values are scaled by factor of 100, such that a 40 kt (~20 m s^-1) wind speed and a 12 g kg^-1 mixing ratio (0.012 g g^-1) results in a moisture transport of 24 m s^-1 (the first pink shade in the color fill). High values of moisture transport have been related to heavy rainfall potential with convective systems.

Reference:
Junker, N. M., R. S. Schneider, and S. L. Fauver, 1999: A study of heavy rainfall events during the great Midwest flood of 1993. Wea. Forecasting, 14, 701-712.