The 850 mb moisture transport is the product of the wind speed (m/s) and the mixing ratio (g/g) at 850 mb. Values are scaled by factor of 100, such that a 40 kt (~20 m/s) wind speed and a 12 g/kg mixing ratio (0.012 g/g) results in a moisture transport of 24 m/s (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.