As Victor and msabin state, the solid amber (red) color for the 11A/N or 11B/G/N LEDs means the radio is enabled, however HT is not enabled.
To enable on the IAP make sure you have not enabled Legacy Only for 2.4 and 5.GHz radios (Under RF --> Advanced Options --> Radio Tab. When this is Disabled you enable 802.11n support for the particular radio (this is the default).