@Anonymous User
That's a weird one and not normal IMO, i have heard of a "Leopard changing it's Spots" but not heard before about the NowTV blue logo on the smart box changing colour to a faded white.
How long have you owned the smart box for and where did you buy it from ?
From what i can tell the Now TV logo's looks like to be some kind of vinyl blue coloured type stickers (though i don't know the material used or the process method in applying the logo to the box outer casing).
Usually you find with vinyl coloured stick on labels that the colour tends to fade in UV Sun light and when a high concentrate of heat is involved the glue used tends to lose it's adhesive properties.
If you are not satisfied then i would suggest asking the Retailer where you purchased the box from for a replacement. (see link below about the procedure for returning your box under warranty).
http://help.nowtv.com/article/Return-my-NOW-TV-Box
Like @Anonymous User mentioned the smart box does operate hot and good ventilation around the smart is extremely important for the life expectancy and reliability of the inbuilt electronics.
