the leaves have changed from a glossy dark green to a kind of
pale green yellowy colour.

Don't think the little red 'uns would cause much harm. More likely that
your soil is pH neutral or towards chalky/lime. Bay likes acid soil so
give it a good dose of ericaceous feed, the sort they sell for heathers,
rhododendrons, camellias (and laurel).
Bay is another laurel.
and SWMBO just reminded me that most of our laurel leaves at the front of
the house have turned yellow with brown edges.
Caused by the copious amount of salt spread on the main road nearby, dutring
the winter.
DaveK.