If the TV is displaying a picture obtained from its own (internal) tuner circuitry then it's definitely fault, and you can't fix it yourself. You need to fall back upon your statutory rights. (See below).
But if the TV is displaying a picture from an external source (such as a Sky box) the first thing to do is to check that all of the connections are secure. (A loose Scart lead can cause a colour cast on your screen).
Your TV is within the period when the RETAILER (and NOT the manufacturer) remains responsible for remedying any problem which comes about through an 'inherent fault'. (That means something which was actually wrong with the set at the time of purchase, such as the use of poor quality components or poor workmanship).
Since you've had the set longer than 6 months, you need to show that the most likely cause of the problem is indeed that of an inherent fault. Theoretically you need to get an independent report on the condition of the set to make such a point but, in practice, simply challenging the retailer to suggest any alternative cause of the problem is likely to suffice.
Contact the retailer and demand that the set is either repaired or replaced. (You have the right to state which of those options you'd prefer but the retailer is permitted to substitute the alternative option on the grounds of economic viability).
Chris