BOAC comment is correct. Use of wing anti-ice does not change stall speed but many aircraft re-set stall warning and manuever speeds as a pre-caution.
The assumption is that if wing anti-ice has been activated, there may be ice on the unprotected portions of the wing. If there is ice on the unprotected wing, stall speed could be increased leading to the need to increase stall warning and manuever speeds and a subsequent amber band change.