I do agree with the point that on plastic chrome fittings that after a few years they go yellow.
This is the silver pipe cover on my kitchen rad and the top has turned a yellowy gold. All that can be done is regular replacement (like every 2 years)
Anything plastic and shiny near heat tends to go brown. Even the white covers I used went brown.
But I have to say the plastic pipe clips have faired better.
Ive got these in my house and its the same colour 5 years on