Foreground and background color are saved in a single byte. Bits 0..3 are the foreground color and bits 4..6 are the background color. If the Private->Attribute defined correctly, (Private->Attribute >> 4) must be less than 8. This commit uses ASSERT to assume "Attribute >> 4" is less than 8. Cc: Dandan Bi <dandan.bi@intel.com> Cc: Eric Dong <eric.dong@intel.com> Signed-off-by: Shenglei Zhang <shenglei.zhang@intel.com> Reviewed-by: Dandan Bi <dandan.bi@intel.com>