Seems as if Samsung has changed the offer and at some point when they realised they had messed up and didn't have the correct stock levels of buds available. I am assuming different customers have different terms and conditions. My offer section of the track my claim site clearly states white is the only option.
Participants who pre-order a new (i.e. not second hand) qualifying Samsung product as shown below in Table 1 (a “Promotion Product”) from a Participating Retailer shown in Table 1 below (“Participating Retailer”) in the UK, Channel Islands, Isle of Man or Republic of Ireland within the Promotion Period will be eligible to claim a pair of Samsung Galaxy Buds in white by redemption (the “Reward”)