There's not a lot of detail in your question, is there?
Are you seeing a picture that's got a blue colour cast? (If so, there's probably no way of fixing it yourself)
Or are you just seeing an all-blue screen? That often occurs when there's no input source available. (e.g. your TV is expecting to see the signal from a Sky box, or similar, and there's no signal coming from the relevant device).
If you normally get your TV via an external device (such as a Sky box), check that it's turned on and that the cable between it and your TV hasn't come loose.
If you've done that (or if you've not got an external source anyway), press the 'Source' button on your TV's remote control. (It's often marked by a rounded rectangle with an arrow going into it). Check that the correct source is shown. (For normal TV reception, via an aerial plugged into the back of the set, the source should be something like 'DTV'. For accepting a signal from a Sky box, or similar, it should be something like 'HDMI1'. If in doubt, try all the options!)