yes that should pep it up a bit. It certainly does look as if it is lacking nutrients.

It may need a bigger pot - can't see how big its pot is in this picture. One thing though - I notice black areas on the rim of the pot, is that just staining or a deposit? If this plant has been in the same pot for 2/3 years, time to pot up into something larger with ericaceous compost and that will cause a revival into a healthy green plant in fairly short order.

Please also check beneath the leaves, to make sure there's no presence of cushion scale - this is what that looks like:

https://www.rhs.org.uk/advice/profile?PID=483

Thank you very much indeed for your very helpful replies to my question.

I shall do exactly what has been suggested - much appreciated.