Well, those colors are wind speeds.
Also, see that thing that the top that says "Min MSLP: 869.1mb"? That's the atmospheric pressure inside the storm measured in millibar - the lower it is (1013mb is normal atmospheric pressure right now), the stronger the storm is.
The worst storm ever recorded made landfall with a pressure of 903mbar - if Irma hits with something in the range of 800, it's going to completely decimate anything it rolls through.
Hurricanes are also measured in a unit called "Accumulated Cyclone Energy" - Harvey was rated 11.2 on that scale, Irma is currently rated at 26.9 and rising.