What puts the blue into chlorophyll?

The hot sunny spell has finally brought a full-on spring. All the trees are covered in leaves & the blossoms are blossoming. The candles on the horse chestnuts are large & cream & proud, though not noticeably plentiful. A neighbour planted a lilac a few years ago which hasn’t done much until this year, when it has suddenly produced large, deep purple panicles

But the green is definitely much more yellow than it has been in recent years. Nearer to lime than emerald. This is much more noticeable in the leaves than it is in the grass on the hills

Which set me thinking. If this were paint you would just say: Add more blue

So, what does put the blue into chlorophyll?

Some kind of nutrient which is relatively lacking this year?

Or is it an effect of the light? Somehing in the atmosphere filtering out the blue?

Or just a bit of etiolation due to poor light, too much cloud cover during March & April?

Related post: Has spring sprung?